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 $92.62   5.405%   $97.6261   $97.63   $97.65   $97.60  
  Purchase #2 $48.52   4.553%   $50.7291   $50.73   $50.75   $50.70  
  Purchase #3 $148.90   4.586%   $155.7286   $155.73   $155.75   $155.70  
  Purchase #4 $243.26   3.116%   $250.84   $250.84   $250.85   $250.80  
  Purchase #5 $124.73   10.138%   $137.3751   $137.38   $137.40   $137.40  
  Purchase #6 $118.98   10.310%   $131.2468   $131.25   $131.25   $131.20  
  Purchase #7 $139.39   9.718%   $152.9359   $152.94   $152.95   $152.90  
  7 purchase totals = $916.40       $976.4816   $976.50   $976.60   $976.30