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 $225.66   11.770%   $252.2202   $252.22   $252.20   $252.20  
  Purchase #2 $55.81   6.494%   $59.4343   $59.43   $59.45   $59.40  
  Purchase #3 $233.25   5.719%   $246.5896   $246.59   $246.60   $246.60  
  Purchase #4 $92.83   5.181%   $97.6395   $97.64   $97.65   $97.60  
  Purchase #5 $5.81   11.503%   $6.4783   $6.48   $6.50   $6.50  
  Purchase #6 $139.69   11.499%   $155.753   $155.75   $155.75   $155.80  
  Purchase #7 $26.40   4.816%   $27.6714   $27.67   $27.65   $27.70  
  7 purchase totals = $779.45       $845.7863   $845.78   $845.80   $845.80