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 $201.27   4.621%   $210.5707   $210.57   $210.55   $210.60  
  Purchase #2 $100.65   3.368%   $104.0399   $104.04   $104.05   $104.00  
  Purchase #3 $234.32   10.372%   $258.6237   $258.62   $258.60   $258.60  
  Purchase #4 $171.73   13.236%   $194.4602   $194.46   $194.45   $194.50  
  Purchase #5 $53.51   10.433%   $59.0927   $59.09   $59.10   $59.10  
  Purchase #6 $184.82   5.491%   $194.9685   $194.97   $194.95   $195.00  
  Purchase #7 $216.50   6.776%   $231.17   $231.17   $231.15   $231.20  
  7 purchase totals = $1,162.80       $1,252.9257   $1,252.92   $1,252.85   $1,253.00