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 $81.52   13.147%   $92.2374   $92.24   $92.25   $92.20  
  Purchase #2 $204.94   8.545%   $222.4521   $222.45   $222.45   $222.50  
  Purchase #3 $23.73   13.560%   $26.9478   $26.95   $26.95   $26.90  
  Purchase #4 $239.97   5.556%   $253.3027   $253.30   $253.30   $253.30  
  Purchase #5 $56.63   13.219%   $64.1159   $64.12   $64.10   $64.10  
  Purchase #6 $155.66   10.840%   $172.5335   $172.53   $172.55   $172.50  
  Purchase #7 $40.58   4.821%   $42.5364   $42.54   $42.55   $42.50  
  7 purchase totals = $803.03       $874.1258   $874.13   $874.15   $874.00