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 $118.92   6.835%   $127.0482   $127.05   $127.05   $127.00  
  Purchase #2 $191.98   6.744%   $204.9271   $204.93   $204.95   $204.90  
  Purchase #3 $136.49   10.827%   $151.2678   $151.27   $151.25   $151.30  
  Purchase #4 $161.34   11.259%   $179.5053   $179.51   $179.50   $179.50  
  Purchase #5 $26.91   11.302%   $29.9514   $29.95   $29.95   $30.00  
  Purchase #6 $189.78   3.622%   $196.6538   $196.65   $196.65   $196.70  
  Purchase #7 $70.30   10.444%   $77.6421   $77.64   $77.65   $77.60  
  7 purchase totals = $895.72       $966.9957   $967.00   $967.00   $967.00