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 $194.54   6.274%   $206.7454   $206.75   $206.75   $206.70  
  Purchase #2 $189.61   3.660%   $196.5497   $196.55   $196.55   $196.50  
  Purchase #3 $36.33   4.727%   $38.0473   $38.05   $38.05   $38.00  
  Purchase #4 $137.29   9.539%   $150.3861   $150.39   $150.40   $150.40  
  Purchase #5 $229.30   6.180%   $243.4707   $243.47   $243.45   $243.50  
  Purchase #6 $56.35   3.584%   $58.3696   $58.37   $58.35   $58.40  
  Purchase #7 $25.61   3.367%   $26.4723   $26.47   $26.45   $26.50  
  7 purchase totals = $869.03       $920.0411   $920.05   $920.00   $920.00