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 $86.89   8.841%   $94.5719   $94.57   $94.55   $94.60  
  Purchase #2 $42.45   12.798%   $47.8828   $47.88   $47.90   $47.90  
  Purchase #3 $195.62   7.562%   $210.4128   $210.41   $210.40   $210.40  
  Purchase #4 $89.29   6.484%   $95.0796   $95.08   $95.10   $95.10  
  Purchase #5 $19.94   3.445%   $20.6269   $20.63   $20.65   $20.60  
  Purchase #6 $182.88   13.481%   $207.5341   $207.53   $207.55   $207.50  
  Purchase #7 $192.28   3.700%   $199.3944   $199.39   $199.40   $199.40  
  7 purchase totals = $809.35       $875.5025   $875.49   $875.55   $875.50