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 $83.59   12.841%   $94.3238   $94.32   $94.30   $94.30  
  Purchase #2 $204.84   7.290%   $219.7728   $219.77   $219.75   $219.80  
  Purchase #3 $213.48   12.300%   $239.738   $239.74   $239.75   $239.70  
  Purchase #4 $43.71   3.240%   $45.1262   $45.13   $45.15   $45.10  
  Purchase #5 $52.98   7.695%   $57.0568   $57.06   $57.05   $57.10  
  Purchase #6 $29.40   3.589%   $30.4552   $30.46   $30.45   $30.50  
  Purchase #7 $37.89   6.395%   $40.3131   $40.31   $40.30   $40.30  
  7 purchase totals = $665.89       $726.7859   $726.79   $726.75   $726.80