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 $94.56   10.424%   $104.4169   $104.42   $104.40   $104.40  
  Purchase #2 $177.30   8.703%   $192.7304   $192.73   $192.75   $192.70  
  Purchase #3 $91.83   4.455%   $95.921   $95.92   $95.90   $95.90  
  Purchase #4 $210.75   9.651%   $231.0895   $231.09   $231.10   $231.10  
  Purchase #5 $72.31   3.659%   $74.9558   $74.96   $74.95   $75.00  
  Purchase #6 $41.56   12.348%   $46.6918   $46.69   $46.70   $46.70  
  Purchase #7 $192.66   8.581%   $209.1922   $209.19   $209.20   $209.20  
  7 purchase totals = $880.97       $954.9976   $955.00   $955.00   $955.00