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 $244.93   8.194%   $264.9996   $265.00   $265.00   $265.00  
  Purchase #2 $235.35   12.674%   $265.1783   $265.18   $265.20   $265.20  
  Purchase #3 $207.74   9.753%   $228.0009   $228.00   $228.00   $228.00  
  Purchase #4 $109.90   11.499%   $122.5374   $122.54   $122.55   $122.50  
  Purchase #5 $52.71   4.193%   $54.9201   $54.92   $54.90   $54.90  
  Purchase #6 $206.45   3.389%   $213.4466   $213.45   $213.45   $213.40  
  Purchase #7 $200.44   10.361%   $221.2076   $221.21   $221.20   $221.20  
  7 purchase totals = $1,257.52       $1,370.2905   $1,370.30   $1,370.30   $1,370.20