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 $64.93   5.466%   $68.4791   $68.48   $68.50   $68.50  
  Purchase #2 $191.33   9.588%   $209.6747   $209.67   $209.65   $209.70  
  Purchase #3 $122.75   11.348%   $136.6797   $136.68   $136.70   $136.70  
  Purchase #4 $219.71   10.621%   $243.0454   $243.05   $243.05   $243.00  
  Purchase #5 $167.68   11.577%   $187.0923   $187.09   $187.10   $187.10  
  Purchase #6 $242.38   10.541%   $267.9293   $267.93   $267.95   $267.90  
  Purchase #7 $109.72   12.770%   $123.7312   $123.73   $123.75   $123.70  
  7 purchase totals = $1,118.50       $1,236.6317   $1,236.63   $1,236.70   $1,236.60