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 $56.71   5.420%   $59.7837   $59.78   $59.80   $59.80  
  Purchase #2 $205.58   8.766%   $223.6011   $223.60   $223.60   $223.60  
  Purchase #3 $196.78   3.341%   $203.3544   $203.35   $203.35   $203.40  
  Purchase #4 $94.76   6.509%   $100.9279   $100.93   $100.95   $100.90  
  Purchase #5 $187.66   10.702%   $207.7434   $207.74   $207.75   $207.70  
  Purchase #6 $69.79   9.544%   $76.4508   $76.45   $76.45   $76.50  
  Purchase #7 $90.52   11.687%   $101.0991   $101.10   $101.10   $101.10  
  7 purchase totals = $901.80       $972.9604   $972.95   $973.00   $973.00