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 $248.91   10.532%   $275.1252   $275.13   $275.15   $275.10  
  Purchase #2 $64.67   4.154%   $67.3564   $67.36   $67.35   $67.40  
  Purchase #3 $204.53   6.243%   $217.2988   $217.30   $217.30   $217.30  
  Purchase #4 $178.59   8.185%   $193.2076   $193.21   $193.20   $193.20  
  Purchase #5 $195.50   7.394%   $209.9553   $209.96   $209.95   $210.00  
  Purchase #6 $192.70   6.319%   $204.8767   $204.88   $204.90   $204.90  
  Purchase #7 $34.52   9.306%   $37.7324   $37.73   $37.75   $37.70  
  7 purchase totals = $1,119.42       $1,205.5524   $1,205.57   $1,205.60   $1,205.60