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 $208.86   10.354%   $230.4854   $230.49   $230.50   $230.50  
  Purchase #2 $87.76   8.723%   $95.4153   $95.42   $95.40   $95.40  
  Purchase #3 $64.91   6.479%   $69.1155   $69.12   $69.10   $69.10  
  Purchase #4 $198.44   3.143%   $204.677   $204.68   $204.70   $204.70  
  Purchase #5 $13.81   7.284%   $14.8159   $14.82   $14.80   $14.80  
  Purchase #6 $159.59   5.345%   $168.1201   $168.12   $168.10   $168.10  
  Purchase #7 $241.33   10.196%   $265.936   $265.94   $265.95   $265.90  
  7 purchase totals = $974.70       $1,048.5652   $1,048.59   $1,048.55   $1,048.50