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 $56.43   4.426%   $58.9276   $58.93   $58.95   $58.90  
  Purchase #2 $194.38   5.522%   $205.1137   $205.11   $205.10   $205.10  
  Purchase #3 $27.29   8.162%   $29.5174   $29.52   $29.50   $29.50  
  Purchase #4 $157.38   3.352%   $162.6554   $162.66   $162.65   $162.70  
  Purchase #5 $155.85   3.784%   $161.7474   $161.75   $161.75   $161.70  
  Purchase #6 $195.29   11.438%   $217.6273   $217.63   $217.65   $217.60  
  Purchase #7 $189.50   5.710%   $200.3205   $200.32   $200.30   $200.30  
  7 purchase totals = $976.12       $1,035.9093   $1,035.92   $1,035.90   $1,035.80