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 $243.43   9.819%   $267.3324   $267.33   $267.35   $267.30  
  Purchase #2 $159.47   11.575%   $177.9287   $177.93   $177.95   $177.90  
  Purchase #3 $161.65   9.275%   $176.643   $176.64   $176.65   $176.60  
  Purchase #4 $219.37   5.643%   $231.749   $231.75   $231.75   $231.70  
  Purchase #5 $233.71   3.648%   $242.2357   $242.24   $242.25   $242.20  
  Purchase #6 $56.91   6.348%   $60.5226   $60.52   $60.50   $60.50  
  Purchase #7 $180.90   5.608%   $191.0449   $191.04   $191.05   $191.00  
  7 purchase totals = $1,255.44       $1,347.4563   $1,347.45   $1,347.50   $1,347.20