Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $238.61   10.682%   $264.0983   $264.10   $264.10   $264.10  
  Purchase #2 $162.47   11.837%   $181.7016   $181.70   $181.70   $181.70  
  Purchase #3 $184.94   13.766%   $210.3988   $210.40   $210.40   $210.40  
  Purchase #4 $218.92   10.231%   $241.3177   $241.32   $241.30   $241.30  
  Purchase #5 $103.93   4.552%   $108.6609   $108.66   $108.65   $108.70  
  Purchase #6 $211.39   7.109%   $226.4177   $226.42   $226.40   $226.40  
  Purchase #7 $120.96   3.496%   $125.1888   $125.19   $125.20   $125.20  
  7 purchase totals = $1,241.22       $1,357.7838   $1,357.79   $1,357.75   $1,357.80