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 $242.31   10.693%   $268.2202   $268.22   $268.20   $268.20  
  Purchase #2 $121.93   9.370%   $133.3548   $133.35   $133.35   $133.40  
  Purchase #3 $158.83   3.444%   $164.3001   $164.30   $164.30   $164.30  
  Purchase #4 $108.98   8.801%   $118.5713   $118.57   $118.55   $118.60  
  Purchase #5 $79.36   9.177%   $86.6429   $86.64   $86.65   $86.60  
  Purchase #6 $188.92   11.198%   $210.0753   $210.08   $210.10   $210.10  
  Purchase #7 $135.34   8.229%   $146.4771   $146.48   $146.50   $146.50  
  7 purchase totals = $1,035.67       $1,127.6417   $1,127.64   $1,127.65   $1,127.70