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 $237.68   5.410%   $250.5385   $250.54   $250.55   $250.50  
  Purchase #2 $225.55   12.439%   $253.6062   $253.61   $253.60   $253.60  
  Purchase #3 $145.63   3.824%   $151.1989   $151.20   $151.20   $151.20  
  Purchase #4 $60.57   3.614%   $62.759   $62.76   $62.75   $62.80  
  Purchase #5 $194.95   6.495%   $207.612   $207.61   $207.60   $207.60  
  Purchase #6 $26.92   6.740%   $28.7344   $28.73   $28.75   $28.70  
  Purchase #7 $55.53   12.704%   $62.5845   $62.58   $62.60   $62.60  
  7 purchase totals = $946.83       $1,017.0335   $1,017.03   $1,017.05   $1,017.00