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 $124.79   8.126%   $134.9304   $134.93   $134.95   $134.90  
  Purchase #2 $176.48   5.596%   $186.3558   $186.36   $186.35   $186.40  
  Purchase #3 $231.88   9.547%   $254.0176   $254.02   $254.00   $254.00  
  Purchase #4 $14.42   7.257%   $15.4665   $15.47   $15.45   $15.50  
  Purchase #5 $177.78   6.684%   $189.6628   $189.66   $189.65   $189.70  
  Purchase #6 $212.90   11.147%   $236.632   $236.63   $236.65   $236.60  
  Purchase #7 $78.85   5.847%   $83.4604   $83.46   $83.45   $83.50  
  7 purchase totals = $1,017.10       $1,100.5255   $1,100.53   $1,100.50   $1,100.60