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 $82.80   13.484%   $93.9648   $93.96   $93.95   $94.00  
  Purchase #2 $198.46   9.393%   $217.1013   $217.10   $217.10   $217.10  
  Purchase #3 $189.76   11.376%   $211.3471   $211.35   $211.35   $211.30  
  Purchase #4 $201.69   5.616%   $213.0169   $213.02   $213.00   $213.00  
  Purchase #5 $234.82   9.448%   $257.0058   $257.01   $257.00   $257.00  
  Purchase #6 $31.44   6.599%   $33.5147   $33.51   $33.50   $33.50  
  Purchase #7 $135.77   11.162%   $150.9246   $150.92   $150.90   $150.90  
  7 purchase totals = $1,074.74       $1,176.8752   $1,176.87   $1,176.80   $1,176.80