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 $61.25   8.860%   $66.6768   $66.68   $66.70   $66.70  
  Purchase #2 $224.71   9.251%   $245.4979   $245.50   $245.50   $245.50  
  Purchase #3 $245.70   3.112%   $253.3462   $253.35   $253.35   $253.30  
  Purchase #4 $231.86   6.359%   $246.604   $246.60   $246.60   $246.60  
  Purchase #5 $57.97   7.583%   $62.3659   $62.37   $62.35   $62.40  
  Purchase #6 $173.92   7.474%   $186.9188   $186.92   $186.90   $186.90  
  Purchase #7 $169.88   9.561%   $186.1222   $186.12   $186.10   $186.10  
  7 purchase totals = $1,165.29       $1,247.5318   $1,247.54   $1,247.50   $1,247.50