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 $46.47   13.370%   $52.683   $52.68   $52.70   $52.70  
  Purchase #2 $117.40   13.283%   $132.9942   $132.99   $133.00   $133.00  
  Purchase #3 $26.30   13.336%   $29.8074   $29.81   $29.80   $29.80  
  Purchase #4 $154.65   13.421%   $175.4056   $175.41   $175.40   $175.40  
  Purchase #5 $38.95   4.340%   $40.6404   $40.64   $40.65   $40.60  
  Purchase #6 $181.73   11.410%   $202.4654   $202.47   $202.45   $202.50  
  Purchase #7 $84.85   8.398%   $91.9757   $91.98   $92.00   $92.00  
  7 purchase totals = $650.35       $725.9717   $725.98   $726.00   $726.00