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 $92.68   5.796%   $98.0517   $98.05   $98.05   $98.10  
  Purchase #2 $112.60   11.401%   $125.4375   $125.44   $125.45   $125.40  
  Purchase #3 $151.41   10.781%   $167.7335   $167.73   $167.75   $167.70  
  Purchase #4 $238.58   3.479%   $246.8802   $246.88   $246.90   $246.90  
  Purchase #5 $140.96   4.736%   $147.6359   $147.64   $147.65   $147.60  
  Purchase #6 $163.96   10.848%   $181.7464   $181.75   $181.75   $181.70  
  Purchase #7 $16.65   8.556%   $18.0746   $18.07   $18.05   $18.10  
  7 purchase totals = $916.84       $985.5598   $985.56   $985.60   $985.50