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 $26.44   4.660%   $27.6721   $27.67   $27.65   $27.70  
  Purchase #2 $225.98   9.614%   $247.7057   $247.71   $247.70   $247.70  
  Purchase #3 $94.36   6.393%   $100.3924   $100.39   $100.40   $100.40  
  Purchase #4 $240.32   11.818%   $268.721   $268.72   $268.70   $268.70  
  Purchase #5 $55.37   8.642%   $60.1551   $60.16   $60.15   $60.20  
  Purchase #6 $203.64   3.373%   $210.5088   $210.51   $210.50   $210.50  
  Purchase #7 $217.55   12.279%   $244.263   $244.26   $244.25   $244.30  
  7 purchase totals = $1,063.66       $1,159.4181   $1,159.42   $1,159.35   $1,159.50