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 $222.64   13.521%   $252.7432   $252.74   $252.75   $252.70  
  Purchase #2 $124.67   10.532%   $137.8002   $137.80   $137.80   $137.80  
  Purchase #3 $169.99   8.188%   $183.9088   $183.91   $183.90   $183.90  
  Purchase #4 $231.98   9.211%   $253.3477   $253.35   $253.35   $253.30  
  Purchase #5 $209.56   10.159%   $230.8492   $230.85   $230.85   $230.80  
  Purchase #6 $56.68   10.171%   $62.4449   $62.44   $62.45   $62.40  
  Purchase #7 $141.47   8.176%   $153.0366   $153.04   $153.05   $153.00  
  7 purchase totals = $1,156.99       $1,274.1306   $1,274.13   $1,274.15   $1,273.90