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 $133.80   3.490%   $138.4696   $138.47   $138.45   $138.50  
  Purchase #2 $119.48   12.473%   $134.3827   $134.38   $134.40   $134.40  
  Purchase #3 $18.94   6.413%   $20.1546   $20.15   $20.15   $20.20  
  Purchase #4 $171.32   3.410%   $177.162   $177.16   $177.15   $177.20  
  Purchase #5 $31.39   9.758%   $34.453   $34.45   $34.45   $34.50  
  Purchase #6 $85.75   13.625%   $97.4334   $97.43   $97.45   $97.40  
  Purchase #7 $122.45   9.643%   $134.2579   $134.26   $134.25   $134.30  
  7 purchase totals = $683.13       $736.3132   $736.30   $736.30   $736.50