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 $69.44   6.370%   $73.8633   $73.86   $73.85   $73.90  
  Purchase #2 $232.97   9.576%   $255.2792   $255.28   $255.30   $255.30  
  Purchase #3 $86.41   10.325%   $95.3318   $95.33   $95.35   $95.30  
  Purchase #4 $50.95   8.747%   $55.4066   $55.41   $55.40   $55.40  
  Purchase #5 $71.84   12.275%   $80.6584   $80.66   $80.65   $80.70  
  Purchase #6 $152.32   13.723%   $173.2229   $173.22   $173.20   $173.20  
  Purchase #7 $249.54   11.276%   $277.6781   $277.68   $277.70   $277.70  
  7 purchase totals = $913.47       $1,011.4403   $1,011.44   $1,011.45   $1,011.50