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 $74.87   9.738%   $82.1608   $82.16   $82.15   $82.20  
  Purchase #2 $159.84   11.848%   $178.7778   $178.78   $178.80   $178.80  
  Purchase #3 $182.69   3.465%   $189.0202   $189.02   $189.00   $189.00  
  Purchase #4 $6.89   12.772%   $7.77   $7.77   $7.75   $7.80  
  Purchase #5 $35.28   12.216%   $39.5898   $39.59   $39.60   $39.60  
  Purchase #6 $205.56   7.229%   $220.4199   $220.42   $220.40   $220.40  
  Purchase #7 $53.66   6.327%   $57.0551   $57.06   $57.05   $57.10  
  7 purchase totals = $718.79       $774.7936   $774.80   $774.75   $774.90