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 $246.68   3.854%   $256.187   $256.19   $256.20   $256.20  
  Purchase #2 $80.84   9.609%   $88.6079   $88.61   $88.60   $88.60  
  Purchase #3 $168.68   10.717%   $186.7574   $186.76   $186.75   $186.80  
  Purchase #4 $126.45   4.794%   $132.512   $132.51   $132.50   $132.50  
  Purchase #5 $17.99   11.536%   $20.0653   $20.07   $20.05   $20.10  
  Purchase #6 $11.90   3.748%   $12.346   $12.35   $12.35   $12.30  
  Purchase #7 $55.64   13.761%   $63.2966   $63.30   $63.30   $63.30  
  7 purchase totals = $708.18       $759.7722   $759.79   $759.75   $759.80