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 $41.70   13.454%   $47.3103   $47.31   $47.30   $47.30  
  Purchase #2 $247.60   8.583%   $268.8515   $268.85   $268.85   $268.90  
  Purchase #3 $189.77   3.289%   $196.0115   $196.01   $196.00   $196.00  
  Purchase #4 $206.54   5.254%   $217.3916   $217.39   $217.40   $217.40  
  Purchase #5 $204.38   6.250%   $217.1538   $217.15   $217.15   $217.20  
  Purchase #6 $231.98   13.497%   $263.2903   $263.29   $263.30   $263.30  
  Purchase #7 $190.44   13.808%   $216.736   $216.74   $216.75   $216.70  
  7 purchase totals = $1,312.41       $1,426.7450   $1,426.74   $1,426.75   $1,426.80