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 $124.41   7.389%   $133.6027   $133.60   $133.60   $133.60  
  Purchase #2 $190.62   6.216%   $202.4689   $202.47   $202.45   $202.50  
  Purchase #3 $117.73   4.644%   $123.1974   $123.20   $123.20   $123.20  
  Purchase #4 $219.50   5.461%   $231.4869   $231.49   $231.50   $231.50  
  Purchase #5 $40.71   9.747%   $44.678   $44.68   $44.70   $44.70  
  Purchase #6 $55.52   10.559%   $61.3824   $61.38   $61.40   $61.40  
  Purchase #7 $58.59   11.177%   $65.1386   $65.14   $65.15   $65.10  
  7 purchase totals = $807.08       $861.9549   $861.96   $862.00   $862.00