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 $232.87   13.440%   $264.1677   $264.17   $264.15   $264.20  
  Purchase #2 $220.52   10.448%   $243.5599   $243.56   $243.55   $243.60  
  Purchase #3 $82.64   4.622%   $86.4596   $86.46   $86.45   $86.50  
  Purchase #4 $195.90   10.765%   $216.9886   $216.99   $217.00   $217.00  
  Purchase #5 $28.38   10.809%   $31.4476   $31.45   $31.45   $31.40  
  Purchase #6 $202.56   6.167%   $215.0519   $215.05   $215.05   $215.10  
  Purchase #7 $198.91   3.687%   $206.2438   $206.24   $206.25   $206.20  
  7 purchase totals = $1,161.78       $1,263.9191   $1,263.92   $1,263.90   $1,264.00