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 $169.32   13.175%   $191.6279   $191.63   $191.65   $191.60  
  Purchase #2 $230.75   11.281%   $256.7809   $256.78   $256.80   $256.80  
  Purchase #3 $244.73   11.637%   $273.2092   $273.21   $273.20   $273.20  
  Purchase #4 $169.30   12.725%   $190.8434   $190.84   $190.85   $190.80  
  Purchase #5 $22.86   10.611%   $25.2857   $25.29   $25.30   $25.30  
  Purchase #6 $65.92   10.662%   $72.9484   $72.95   $72.95   $72.90  
  Purchase #7 $203.30   13.632%   $231.0139   $231.01   $231.00   $231.00  
  7 purchase totals = $1,106.18       $1,241.7094   $1,241.71   $1,241.75   $1,241.60