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 $239.44   11.858%   $267.8328   $267.83   $267.85   $267.80  
  Purchase #2 $119.46   4.275%   $124.5669   $124.57   $124.55   $124.60  
  Purchase #3 $109.43   6.759%   $116.8264   $116.83   $116.85   $116.80  
  Purchase #4 $123.95   13.844%   $141.1096   $141.11   $141.10   $141.10  
  Purchase #5 $208.81   5.304%   $219.8853   $219.89   $219.90   $219.90  
  Purchase #6 $212.84   7.490%   $228.7817   $228.78   $228.80   $228.80  
  Purchase #7 $149.50   11.667%   $166.9422   $166.94   $166.95   $166.90  
  7 purchase totals = $1,163.43       $1,265.9449   $1,265.95   $1,266.00   $1,265.90