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 $26.69   10.719%   $29.5509   $29.55   $29.55   $29.60  
  Purchase #2 $136.87   10.348%   $151.0333   $151.03   $151.05   $151.00  
  Purchase #3 $173.49   10.701%   $192.0552   $192.06   $192.05   $192.10  
  Purchase #4 $243.25   9.766%   $267.0058   $267.01   $267.00   $267.00  
  Purchase #5 $159.44   13.843%   $181.5113   $181.51   $181.50   $181.50  
  Purchase #6 $196.41   4.554%   $205.3545   $205.35   $205.35   $205.40  
  Purchase #7 $229.55   3.389%   $237.3294   $237.33   $237.35   $237.30  
  7 purchase totals = $1,165.70       $1,263.8404   $1,263.84   $1,263.85   $1,263.90