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 $55.90   11.873%   $62.537   $62.54   $62.55   $62.50  
  Purchase #2 $21.43   13.702%   $24.3663   $24.37   $24.35   $24.40  
  Purchase #3 $95.98   7.431%   $103.1123   $103.11   $103.10   $103.10  
  Purchase #4 $238.46   10.250%   $262.9022   $262.90   $262.90   $262.90  
  Purchase #5 $25.67   13.203%   $29.0592   $29.06   $29.05   $29.10  
  Purchase #6 $191.68   4.537%   $200.3765   $200.38   $200.40   $200.40  
  Purchase #7 $73.97   13.570%   $84.0077   $84.01   $84.00   $84.00  
  7 purchase totals = $703.09       $766.3612   $766.37   $766.35   $766.40