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 $65.86   13.815%   $74.9586   $74.96   $74.95   $75.00  
  Purchase #2 $249.25   9.483%   $272.8864   $272.89   $272.90   $272.90  
  Purchase #3 $209.77   6.158%   $222.6876   $222.69   $222.70   $222.70  
  Purchase #4 $163.92   7.607%   $176.3894   $176.39   $176.40   $176.40  
  Purchase #5 $67.50   6.407%   $71.8247   $71.82   $71.80   $71.80  
  Purchase #6 $204.78   10.863%   $227.0253   $227.03   $227.05   $227.00  
  Purchase #7 $27.91   11.834%   $31.2129   $31.21   $31.20   $31.20  
  7 purchase totals = $988.99       $1,076.9849   $1,076.99   $1,077.00   $1,077.00