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 $88.26   11.592%   $98.4911   $98.49   $98.50   $98.50  
  Purchase #2 $166.90   11.792%   $186.5808   $186.58   $186.60   $186.60  
  Purchase #3 $184.41   5.183%   $193.968   $193.97   $193.95   $194.00  
  Purchase #4 $170.67   7.262%   $183.0641   $183.06   $183.05   $183.10  
  Purchase #5 $166.52   4.410%   $173.8635   $173.86   $173.85   $173.90  
  Purchase #6 $247.96   13.209%   $280.713   $280.71   $280.70   $280.70  
  Purchase #7 $98.64   9.105%   $107.6212   $107.62   $107.60   $107.60  
  7 purchase totals = $1,123.36       $1,224.3017   $1,224.29   $1,224.25   $1,224.40