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 $57.72   9.236%   $63.051   $63.05   $63.05   $63.10  
  Purchase #2 $114.33   10.167%   $125.9539   $125.95   $125.95   $126.00  
  Purchase #3 $23.56   6.107%   $24.9988   $25.00   $25.00   $25.00  
  Purchase #4 $239.66   11.404%   $266.9908   $266.99   $267.00   $267.00  
  Purchase #5 $131.68   11.459%   $146.7692   $146.77   $146.75   $146.80  
  Purchase #6 $14.78   11.501%   $16.4798   $16.48   $16.50   $16.50  
  Purchase #7 $195.60   4.233%   $203.8797   $203.88   $203.90   $203.90  
  7 purchase totals = $777.33       $848.1232   $848.12   $848.15   $848.30