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 $242.33   10.293%   $267.273   $267.27   $267.25   $267.30  
  Purchase #2 $207.55   10.480%   $229.3012   $229.30   $229.30   $229.30  
  Purchase #3 $66.85   10.436%   $73.8265   $73.83   $73.85   $73.80  
  Purchase #4 $249.96   3.231%   $258.0362   $258.04   $258.05   $258.00  
  Purchase #5 $16.27   6.287%   $17.2929   $17.29   $17.30   $17.30  
  Purchase #6 $236.44   6.139%   $250.9551   $250.96   $250.95   $251.00  
  Purchase #7 $116.93   5.682%   $123.574   $123.57   $123.55   $123.60  
  7 purchase totals = $1,136.33       $1,220.2589   $1,220.26   $1,220.25   $1,220.30