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 $230.55   12.462%   $259.2811   $259.28   $259.30   $259.30  
  Purchase #2 $159.87   13.559%   $181.5468   $181.55   $181.55   $181.50  
  Purchase #3 $90.28   7.141%   $96.7269   $96.73   $96.75   $96.70  
  Purchase #4 $210.42   11.856%   $235.3674   $235.37   $235.35   $235.40  
  Purchase #5 $91.32   8.236%   $98.8411   $98.84   $98.85   $98.80  
  Purchase #6 $50.49   3.366%   $52.1895   $52.19   $52.20   $52.20  
  Purchase #7 $217.84   8.825%   $237.0644   $237.06   $237.05   $237.10  
  7 purchase totals = $1,050.77       $1,161.0172   $1,161.02   $1,161.05   $1,161.00