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 $52.38   8.517%   $56.8412   $56.84   $56.85   $56.80  
  Purchase #2 $222.50   13.811%   $253.2295   $253.23   $253.25   $253.20  
  Purchase #3 $116.31   4.615%   $121.6777   $121.68   $121.70   $121.70  
  Purchase #4 $204.54   6.522%   $217.8801   $217.88   $217.90   $217.90  
  Purchase #5 $136.78   13.587%   $155.3643   $155.36   $155.35   $155.40  
  Purchase #6 $239.70   6.873%   $256.1746   $256.17   $256.15   $256.20  
  Purchase #7 $13.92   10.598%   $15.3952   $15.40   $15.40   $15.40  
  7 purchase totals = $986.13       $1,076.5626   $1,076.56   $1,076.60   $1,076.60