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 $136.94   11.252%   $152.3485   $152.35   $152.35   $152.30  
  Purchase #2 $6.78   9.208%   $7.4043   $7.40   $7.40   $7.40  
  Purchase #3 $156.95   12.165%   $176.043   $176.04   $176.05   $176.00  
  Purchase #4 $177.67   6.216%   $188.714   $188.71   $188.70   $188.70  
  Purchase #5 $250.25   5.350%   $263.6384   $263.64   $263.65   $263.60  
  Purchase #6 $89.80   5.748%   $94.9617   $94.96   $94.95   $95.00  
  Purchase #7 $85.27   4.275%   $88.9153   $88.92   $88.90   $88.90  
  7 purchase totals = $903.66       $972.0252   $972.02   $972.00   $971.90