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 $43.63   10.156%   $48.0611   $48.06   $48.05   $48.10  
  Purchase #2 $206.90   12.562%   $232.8908   $232.89   $232.90   $232.90  
  Purchase #3 $128.42   11.732%   $143.4862   $143.49   $143.50   $143.50  
  Purchase #4 $25.37   7.814%   $27.3524   $27.35   $27.35   $27.40  
  Purchase #5 $155.90   6.146%   $165.4816   $165.48   $165.50   $165.50  
  Purchase #6 $119.52   4.390%   $124.7669   $124.77   $124.75   $124.80  
  Purchase #7 $69.90   9.479%   $76.5258   $76.53   $76.55   $76.50  
  7 purchase totals = $749.64       $818.5648   $818.57   $818.60   $818.70