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 $63.45   7.210%   $68.0247   $68.02   $68.00   $68.00  
  Purchase #2 $79.65   13.683%   $90.5485   $90.55   $90.55   $90.50  
  Purchase #3 $39.93   10.422%   $44.0915   $44.09   $44.10   $44.10  
  Purchase #4 $209.78   7.426%   $225.3583   $225.36   $225.35   $225.40  
  Purchase #5 $62.53   6.364%   $66.5094   $66.51   $66.50   $66.50  
  Purchase #6 $94.91   7.251%   $101.7919   $101.79   $101.80   $101.80  
  Purchase #7 $9.34   9.767%   $10.2522   $10.25   $10.25   $10.30  
  7 purchase totals = $559.59       $606.5765   $606.57   $606.55   $606.60