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 $60.60   8.510%   $65.7571   $65.76   $65.75   $65.80  
  Purchase #2 $10.94   3.869%   $11.3633   $11.36   $11.35   $11.40  
  Purchase #3 $77.57   8.719%   $84.3333   $84.33   $84.35   $84.30  
  Purchase #4 $154.85   3.212%   $159.8238   $159.82   $159.80   $159.80  
  Purchase #5 $239.65   10.560%   $264.957   $264.96   $264.95   $265.00  
  Purchase #6 $49.91   8.745%   $54.2746   $54.27   $54.25   $54.30  
  Purchase #7 $194.72   7.784%   $209.877   $209.88   $209.90   $209.90  
  7 purchase totals = $788.24       $850.3861   $850.38   $850.35   $850.50