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 $60.33   5.332%   $63.5468   $63.55   $63.55   $63.50  
  Purchase #2 $168.57   13.317%   $191.0185   $191.02   $191.00   $191.00  
  Purchase #3 $119.63   9.499%   $130.9937   $130.99   $131.00   $131.00  
  Purchase #4 $68.49   9.343%   $74.889   $74.89   $74.90   $74.90  
  Purchase #5 $103.72   10.735%   $114.8543   $114.85   $114.85   $114.90  
  Purchase #6 $87.84   7.607%   $94.522   $94.52   $94.50   $94.50  
  Purchase #7 $244.66   5.455%   $258.0062   $258.01   $258.00   $258.00  
  7 purchase totals = $853.24       $927.8305   $927.83   $927.80   $927.80