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 $46.76   11.292%   $52.0401   $52.04   $52.05   $52.00  
  Purchase #2 $143.88   8.375%   $155.93   $155.93   $155.95   $155.90  
  Purchase #3 $91.85   8.781%   $99.9153   $99.92   $99.90   $99.90  
  Purchase #4 $119.34   4.599%   $124.8284   $124.83   $124.85   $124.80  
  Purchase #5 $64.75   3.462%   $66.9916   $66.99   $67.00   $67.00  
  Purchase #6 $149.75   4.420%   $156.369   $156.37   $156.35   $156.40  
  Purchase #7 $166.33   5.106%   $174.8228   $174.82   $174.80   $174.80  
  7 purchase totals = $782.66       $830.8972   $830.90   $830.90   $830.80