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 $89.94   8.550%   $97.6299   $97.63   $97.65   $97.60  
  Purchase #2 $165.42   12.350%   $185.8494   $185.85   $185.85   $185.80  
  Purchase #3 $249.44   3.217%   $257.4645   $257.46   $257.45   $257.50  
  Purchase #4 $175.97   13.637%   $199.967   $199.97   $199.95   $200.00  
  Purchase #5 $90.44   5.614%   $95.5173   $95.52   $95.50   $95.50  
  Purchase #6 $240.63   7.240%   $258.0516   $258.05   $258.05   $258.10  
  Purchase #7 $206.71   8.650%   $224.5904   $224.59   $224.60   $224.60  
  7 purchase totals = $1,218.55       $1,319.0701   $1,319.07   $1,319.05   $1,319.10