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 $214.97   4.771%   $225.2262   $225.23   $225.25   $225.20  
  Purchase #2 $52.57   8.548%   $57.0637   $57.06   $57.05   $57.10  
  Purchase #3 $56.81   3.840%   $58.9915   $58.99   $59.00   $59.00  
  Purchase #4 $104.78   11.819%   $117.1639   $117.16   $117.15   $117.20  
  Purchase #5 $225.76   12.713%   $254.4609   $254.46   $254.45   $254.50  
  Purchase #6 $67.27   13.509%   $76.3575   $76.36   $76.35   $76.40  
  Purchase #7 $228.72   6.111%   $242.6971   $242.70   $242.70   $242.70  
  7 purchase totals = $950.88       $1,031.9608   $1,031.96   $1,031.95   $1,032.10