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 $21.37   10.728%   $23.6626   $23.66   $23.65   $23.70  
  Purchase #2 $231.90   13.691%   $263.6494   $263.65   $263.65   $263.60  
  Purchase #3 $217.32   4.782%   $227.7122   $227.71   $227.70   $227.70  
  Purchase #4 $59.60   12.261%   $66.9076   $66.91   $66.90   $66.90  
  Purchase #5 $212.88   7.805%   $229.4953   $229.50   $229.50   $229.50  
  Purchase #6 $134.49   12.286%   $151.0134   $151.01   $151.00   $151.00  
  Purchase #7 $61.46   11.580%   $68.5771   $68.58   $68.60   $68.60  
  7 purchase totals = $939.02       $1,031.0176   $1,031.02   $1,031.00   $1,031.00