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 $43.78   12.554%   $49.2761   $49.28   $49.30   $49.30  
  Purchase #2 $209.50   9.583%   $229.5764   $229.58   $229.60   $229.60  
  Purchase #3 $68.32   4.664%   $71.5064   $71.51   $71.50   $71.50  
  Purchase #4 $245.85   11.498%   $274.1178   $274.12   $274.10   $274.10  
  Purchase #5 $113.65   11.522%   $126.7448   $126.74   $126.75   $126.70  
  Purchase #6 $126.69   6.177%   $134.5156   $134.52   $134.50   $134.50  
  Purchase #7 $146.59   13.731%   $166.7183   $166.72   $166.70   $166.70  
  7 purchase totals = $954.38       $1,052.4554   $1,052.47   $1,052.45   $1,052.40