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 $241.47   13.871%   $274.9643   $274.96   $274.95   $275.00  
  Purchase #2 $14.46   12.112%   $16.2114   $16.21   $16.20   $16.20  
  Purchase #3 $44.43   10.465%   $49.0796   $49.08   $49.10   $49.10  
  Purchase #4 $183.28   3.232%   $189.2036   $189.20   $189.20   $189.20  
  Purchase #5 $68.31   4.468%   $71.3621   $71.36   $71.35   $71.40  
  Purchase #6 $240.62   8.163%   $260.2618   $260.26   $260.25   $260.30  
  Purchase #7 $166.27   5.181%   $174.8844   $174.88   $174.90   $174.90  
  7 purchase totals = $958.84       $1,035.9672   $1,035.95   $1,035.95   $1,036.10