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 $227.59   12.763%   $256.6373   $256.64   $256.65   $256.60  
  Purchase #2 $232.95   8.438%   $252.6063   $252.61   $252.60   $252.60  
  Purchase #3 $91.89   5.106%   $96.5819   $96.58   $96.60   $96.60  
  Purchase #4 $243.45   13.746%   $276.9146   $276.91   $276.90   $276.90  
  Purchase #5 $169.34   9.447%   $185.3375   $185.34   $185.35   $185.30  
  Purchase #6 $146.25   3.211%   $150.9461   $150.95   $150.95   $150.90  
  Purchase #7 $243.48   5.210%   $256.1653   $256.17   $256.15   $256.20  
  7 purchase totals = $1,354.95       $1,475.1890   $1,475.20   $1,475.20   $1,475.10