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 $54.53   7.461%   $58.5985   $58.60   $58.60   $58.60  
  Purchase #2 $79.41   10.262%   $87.5591   $87.56   $87.55   $87.60  
  Purchase #3 $58.39   9.528%   $63.9534   $63.95   $63.95   $64.00  
  Purchase #4 $250.25   10.586%   $276.7415   $276.74   $276.75   $276.70  
  Purchase #5 $100.74   4.271%   $105.0426   $105.04   $105.05   $105.00  
  Purchase #6 $167.94   7.510%   $180.5523   $180.55   $180.55   $180.60  
  Purchase #7 $10.96   13.506%   $12.4403   $12.44   $12.45   $12.40  
  7 purchase totals = $722.22       $784.8877   $784.88   $784.90   $784.90