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 $249.51   11.642%   $278.558   $278.56   $278.55   $278.60  
  Purchase #2 $84.54   8.121%   $91.4055   $91.41   $91.40   $91.40  
  Purchase #3 $16.49   5.188%   $17.3455   $17.35   $17.35   $17.30  
  Purchase #4 $213.52   13.530%   $242.4093   $242.41   $242.40   $242.40  
  Purchase #5 $108.42   12.291%   $121.7459   $121.75   $121.75   $121.70  
  Purchase #6 $201.60   6.505%   $214.7141   $214.71   $214.70   $214.70  
  Purchase #7 $88.27   8.595%   $95.8568   $95.86   $95.85   $95.90  
  7 purchase totals = $962.35       $1,062.0351   $1,062.05   $1,062.00   $1,062.00