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 $240.40   10.228%   $264.9881   $264.99   $265.00   $265.00  
  Purchase #2 $60.67   12.321%   $68.1452   $68.15   $68.15   $68.10  
  Purchase #3 $197.69   12.269%   $221.9446   $221.94   $221.95   $221.90  
  Purchase #4 $230.53   6.359%   $245.1894   $245.19   $245.20   $245.20  
  Purchase #5 $169.49   7.770%   $182.6594   $182.66   $182.65   $182.70  
  Purchase #6 $211.94   9.784%   $232.6762   $232.68   $232.70   $232.70  
  Purchase #7 $139.52   6.836%   $149.0576   $149.06   $149.05   $149.10  
  7 purchase totals = $1,250.24       $1,364.6605   $1,364.67   $1,364.70   $1,364.70