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 $216.80   11.147%   $240.9667   $240.97   $240.95   $241.00  
  Purchase #2 $32.42   4.576%   $33.9035   $33.90   $33.90   $33.90  
  Purchase #3 $191.52   5.720%   $202.4749   $202.47   $202.45   $202.50  
  Purchase #4 $167.97   12.600%   $189.1342   $189.13   $189.15   $189.10  
  Purchase #5 $39.93   13.266%   $45.2271   $45.23   $45.25   $45.20  
  Purchase #6 $103.68   10.621%   $114.6919   $114.69   $114.70   $114.70  
  Purchase #7 $180.99   13.111%   $204.7196   $204.72   $204.70   $204.70  
  7 purchase totals = $933.31       $1,031.1179   $1,031.11   $1,031.10   $1,031.10