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 $11.41   6.403%   $12.1406   $12.14   $12.15   $12.10  
  Purchase #2 $231.67   6.863%   $247.5695   $247.57   $247.55   $247.60  
  Purchase #3 $220.43   7.146%   $236.1819   $236.18   $236.20   $236.20  
  Purchase #4 $77.98   11.208%   $86.72   $86.72   $86.70   $86.70  
  Purchase #5 $232.40   13.825%   $264.5293   $264.53   $264.55   $264.50  
  Purchase #6 $43.63   8.788%   $47.4642   $47.46   $47.45   $47.50  
  Purchase #7 $120.93   8.338%   $131.0131   $131.01   $131.00   $131.00  
  7 purchase totals = $938.45       $1,025.6186   $1,025.61   $1,025.60   $1,025.60