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 $98.79   6.226%   $104.9407   $104.94   $104.95   $104.90  
  Purchase #2 $211.33   10.827%   $234.2107   $234.21   $234.20   $234.20  
  Purchase #3 $73.54   13.866%   $83.7371   $83.74   $83.75   $83.70  
  Purchase #4 $213.88   4.201%   $222.8651   $222.87   $222.85   $222.90  
  Purchase #5 $200.79   7.376%   $215.6003   $215.60   $215.60   $215.60  
  Purchase #6 $222.98   11.533%   $248.6963   $248.70   $248.70   $248.70  
  Purchase #7 $41.65   8.301%   $45.1074   $45.11   $45.10   $45.10  
  7 purchase totals = $1,062.96       $1,155.1576   $1,155.17   $1,155.15   $1,155.10