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 $235.58   10.443%   $260.1816   $260.18   $260.20   $260.20  
  Purchase #2 $210.72   11.407%   $234.7568   $234.76   $234.75   $234.80  
  Purchase #3 $71.40   11.158%   $79.3668   $79.37   $79.35   $79.40  
  Purchase #4 $32.67   6.593%   $34.8239   $34.82   $34.80   $34.80  
  Purchase #5 $59.74   6.801%   $63.8029   $63.80   $63.80   $63.80  
  Purchase #6 $50.37   9.232%   $55.0202   $55.02   $55.00   $55.00  
  Purchase #7 $12.63   5.695%   $13.3493   $13.35   $13.35   $13.30  
  7 purchase totals = $673.11       $741.3015   $741.30   $741.25   $741.30