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 $187.86   12.862%   $212.0226   $212.02   $212.00   $212.00  
  Purchase #2 $181.56   9.589%   $198.9698   $198.97   $198.95   $199.00  
  Purchase #3 $239.75   6.356%   $254.9885   $254.99   $255.00   $255.00  
  Purchase #4 $104.34   11.634%   $116.4789   $116.48   $116.50   $116.50  
  Purchase #5 $227.60   7.249%   $244.0987   $244.10   $244.10   $244.10  
  Purchase #6 $111.66   5.293%   $117.5702   $117.57   $117.55   $117.60  
  Purchase #7 $45.88   12.181%   $51.4686   $51.47   $51.45   $51.50  
  7 purchase totals = $1,098.65       $1,195.5973   $1,195.60   $1,195.55   $1,195.70