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 $243.89   5.102%   $256.3333   $256.33   $256.35   $256.30  
  Purchase #2 $212.70   9.354%   $232.596   $232.60   $232.60   $232.60  
  Purchase #3 $59.94   4.513%   $62.6451   $62.65   $62.65   $62.60  
  Purchase #4 $168.73   11.150%   $187.5434   $187.54   $187.55   $187.50  
  Purchase #5 $160.37   10.727%   $177.5729   $177.57   $177.55   $177.60  
  Purchase #6 $204.67   13.466%   $232.2309   $232.23   $232.25   $232.20  
  Purchase #7 $89.55   3.481%   $92.6672   $92.67   $92.65   $92.70  
  7 purchase totals = $1,139.85       $1,241.5888   $1,241.59   $1,241.60   $1,241.50