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 $242.88   8.752%   $264.1369   $264.14   $264.15   $264.10  
  Purchase #2 $63.82   7.602%   $68.6716   $68.67   $68.65   $68.70  
  Purchase #3 $202.60   8.105%   $219.0207   $219.02   $219.00   $219.00  
  Purchase #4 $216.74   8.261%   $234.6449   $234.64   $234.65   $234.60  
  Purchase #5 $207.88   8.549%   $225.6517   $225.65   $225.65   $225.70  
  Purchase #6 $221.53   11.700%   $247.449   $247.45   $247.45   $247.40  
  Purchase #7 $52.92   13.798%   $60.2219   $60.22   $60.20   $60.20  
  7 purchase totals = $1,208.37       $1,319.7967   $1,319.79   $1,319.75   $1,319.70