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 $69.36   11.574%   $77.3877   $77.39   $77.40   $77.40  
  Purchase #2 $250.89   11.243%   $279.0976   $279.10   $279.10   $279.10  
  Purchase #3 $69.91   7.212%   $74.9519   $74.95   $74.95   $75.00  
  Purchase #4 $69.30   8.820%   $75.4123   $75.41   $75.40   $75.40  
  Purchase #5 $195.73   6.191%   $207.8476   $207.85   $207.85   $207.80  
  Purchase #6 $219.63   6.860%   $234.6966   $234.70   $234.70   $234.70  
  Purchase #7 $250.69   11.218%   $278.8124   $278.81   $278.80   $278.80  
  7 purchase totals = $1,125.51       $1,228.2061   $1,228.21   $1,228.20   $1,228.20