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 $46.85   12.144%   $52.5395   $52.54   $52.55   $52.50  
  Purchase #2 $155.89   10.801%   $172.7277   $172.73   $172.75   $172.70  
  Purchase #3 $214.50   12.183%   $240.6325   $240.63   $240.65   $240.60  
  Purchase #4 $179.42   3.301%   $185.3427   $185.34   $185.35   $185.30  
  Purchase #5 $68.47   5.225%   $72.0476   $72.05   $72.05   $72.00  
  Purchase #6 $178.43   11.532%   $199.0065   $199.01   $199.00   $199.00  
  Purchase #7 $201.76   5.596%   $213.0505   $213.05   $213.05   $213.10  
  7 purchase totals = $1,045.32       $1,135.3470   $1,135.35   $1,135.40   $1,135.20