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 $216.94   9.118%   $236.7206   $236.72   $236.70   $236.70  
  Purchase #2 $241.66   5.446%   $254.8208   $254.82   $254.80   $254.80  
  Purchase #3 $101.67   9.108%   $110.9301   $110.93   $110.95   $110.90  
  Purchase #4 $189.31   7.817%   $204.1084   $204.11   $204.10   $204.10  
  Purchase #5 $178.26   8.445%   $193.3141   $193.31   $193.30   $193.30  
  Purchase #6 $221.31   10.363%   $244.2444   $244.24   $244.25   $244.20  
  Purchase #7 $68.55   9.674%   $75.1815   $75.18   $75.20   $75.20  
  7 purchase totals = $1,217.70       $1,319.3199   $1,319.31   $1,319.30   $1,319.20