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 $152.58   4.706%   $159.7604   $159.76   $159.75   $159.80  
  Purchase #2 $227.50   11.625%   $253.9469   $253.95   $253.95   $253.90  
  Purchase #3 $25.25   12.704%   $28.4578   $28.46   $28.45   $28.50  
  Purchase #4 $238.62   13.798%   $271.5448   $271.54   $271.55   $271.50  
  Purchase #5 $186.79   5.599%   $197.2484   $197.25   $197.25   $197.20  
  Purchase #6 $218.28   11.342%   $243.0373   $243.04   $243.05   $243.00  
  Purchase #7 $97.68   8.522%   $106.0043   $106.00   $106.00   $106.00  
  7 purchase totals = $1,146.70       $1,259.9999   $1,260.00   $1,260.00   $1,259.90