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 $110.89   9.677%   $121.6208   $121.62   $121.60   $121.60  
  Purchase #2 $224.37   9.494%   $245.6717   $245.67   $245.65   $245.70  
  Purchase #3 $207.60   3.493%   $214.8515   $214.85   $214.85   $214.90  
  Purchase #4 $17.95   9.868%   $19.7213   $19.72   $19.70   $19.70  
  Purchase #5 $61.45   6.199%   $65.2593   $65.26   $65.25   $65.30  
  Purchase #6 $192.86   13.189%   $218.2963   $218.30   $218.30   $218.30  
  Purchase #7 $137.95   8.637%   $149.8647   $149.86   $149.85   $149.90  
  7 purchase totals = $953.07       $1,035.2856   $1,035.28   $1,035.20   $1,035.40