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 $232.52   5.752%   $245.8946   $245.89   $245.90   $245.90  
  Purchase #2 $50.25   4.181%   $52.351   $52.35   $52.35   $52.40  
  Purchase #3 $24.43   8.267%   $26.4496   $26.45   $26.45   $26.40  
  Purchase #4 $166.79   5.452%   $175.8834   $175.88   $175.90   $175.90  
  Purchase #5 $142.71   3.449%   $147.6321   $147.63   $147.65   $147.60  
  Purchase #6 $230.73   11.407%   $257.0494   $257.05   $257.05   $257.00  
  Purchase #7 $191.69   13.108%   $216.8167   $216.82   $216.80   $216.80  
  7 purchase totals = $1,039.12       $1,122.0768   $1,122.07   $1,122.10   $1,122.00