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 $23.86   11.156%   $26.5218   $26.52   $26.50   $26.50  
  Purchase #2 $226.42   13.126%   $256.1399   $256.14   $256.15   $256.10  
  Purchase #3 $43.82   11.521%   $48.8685   $48.87   $48.85   $48.90  
  Purchase #4 $112.67   3.663%   $116.7971   $116.80   $116.80   $116.80  
  Purchase #5 $82.52   13.457%   $93.6247   $93.62   $93.60   $93.60  
  Purchase #6 $124.91   8.521%   $135.5536   $135.55   $135.55   $135.60  
  Purchase #7 $184.85   3.161%   $190.6931   $190.69   $190.70   $190.70  
  7 purchase totals = $799.05       $868.1987   $868.19   $868.15   $868.20