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 $232.73   13.690%   $264.5907   $264.59   $264.60   $264.60  
  Purchase #2 $72.91   6.362%   $77.5485   $77.55   $77.55   $77.50  
  Purchase #3 $158.48   5.266%   $166.8256   $166.83   $166.85   $166.80  
  Purchase #4 $225.67   7.153%   $241.8122   $241.81   $241.80   $241.80  
  Purchase #5 $198.94   11.556%   $221.9295   $221.93   $221.95   $221.90  
  Purchase #6 $237.88   9.352%   $260.1265   $260.13   $260.15   $260.10  
  Purchase #7 $207.46   4.317%   $216.416   $216.42   $216.40   $216.40  
  7 purchase totals = $1,334.07       $1,449.2490   $1,449.26   $1,449.30   $1,449.10