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 $244.88   12.564%   $275.6467   $275.65   $275.65   $275.60  
  Purchase #2 $213.34   6.320%   $226.8231   $226.82   $226.80   $226.80  
  Purchase #3 $99.91   13.219%   $113.1171   $113.12   $113.10   $113.10  
  Purchase #4 $218.96   11.724%   $244.6309   $244.63   $244.65   $244.60  
  Purchase #5 $9.28   7.124%   $9.9411   $9.94   $9.95   $9.90  
  Purchase #6 $44.66   3.323%   $46.1441   $46.14   $46.15   $46.10  
  Purchase #7 $166.93   10.546%   $184.5344   $184.53   $184.55   $184.50  
  7 purchase totals = $997.96       $1,100.8374   $1,100.83   $1,100.85   $1,100.60