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 $197.99   13.716%   $225.1463   $225.15   $225.15   $225.10  
  Purchase #2 $62.48   9.257%   $68.2638   $68.26   $68.25   $68.30  
  Purchase #3 $177.73   3.639%   $184.1976   $184.20   $184.20   $184.20  
  Purchase #4 $248.67   13.190%   $281.4696   $281.47   $281.45   $281.50  
  Purchase #5 $190.98   5.459%   $201.4056   $201.41   $201.40   $201.40  
  Purchase #6 $182.86   6.706%   $195.1226   $195.12   $195.10   $195.10  
  Purchase #7 $23.54   12.704%   $26.5305   $26.53   $26.55   $26.50  
  7 purchase totals = $1,084.25       $1,182.1360   $1,182.14   $1,182.10   $1,182.10