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 $141.69   10.204%   $156.148   $156.15   $156.15   $156.10  
  Purchase #2 $23.68   4.233%   $24.6824   $24.68   $24.70   $24.70  
  Purchase #3 $60.84   4.107%   $63.3387   $63.34   $63.35   $63.30  
  Purchase #4 $47.78   5.303%   $50.3138   $50.31   $50.30   $50.30  
  Purchase #5 $190.32   9.250%   $207.9246   $207.92   $207.90   $207.90  
  Purchase #6 $56.69   13.705%   $64.4594   $64.46   $64.45   $64.50  
  Purchase #7 $194.30   3.184%   $200.4865   $200.49   $200.50   $200.50  
  7 purchase totals = $715.30       $767.3534   $767.35   $767.35   $767.30