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 $242.55   8.342%   $262.7835   $262.78   $262.80   $262.80  
  Purchase #2 $104.73   4.489%   $109.4313   $109.43   $109.45   $109.40  
  Purchase #3 $37.76   12.401%   $42.4426   $42.44   $42.45   $42.40  
  Purchase #4 $23.96   10.418%   $26.4562   $26.46   $26.45   $26.50  
  Purchase #5 $94.98   6.335%   $100.997   $101.00   $101.00   $101.00  
  Purchase #6 $13.57   5.869%   $14.3664   $14.37   $14.35   $14.40  
  Purchase #7 $206.52   4.614%   $216.0488   $216.05   $216.05   $216.00  
  7 purchase totals = $724.07       $772.5258   $772.53   $772.55   $772.50