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 $219.86   9.688%   $241.16   $241.16   $241.15   $241.20  
  Purchase #2 $67.88   8.575%   $73.7007   $73.70   $73.70   $73.70  
  Purchase #3 $136.99   11.451%   $152.6767   $152.68   $152.70   $152.70  
  Purchase #4 $25.68   7.828%   $27.6902   $27.69   $27.70   $27.70  
  Purchase #5 $197.54   3.442%   $204.3393   $204.34   $204.35   $204.30  
  Purchase #6 $26.40   9.666%   $28.9518   $28.95   $28.95   $29.00  
  Purchase #7 $94.48   9.746%   $103.688   $103.69   $103.70   $103.70  
  7 purchase totals = $768.83       $832.2067   $832.21   $832.25   $832.30