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 $167.32   8.420%   $181.4083   $181.41   $181.40   $181.40  
  Purchase #2 $221.91   5.680%   $234.5145   $234.51   $234.50   $234.50  
  Purchase #3 $22.85   9.354%   $24.9874   $24.99   $25.00   $25.00  
  Purchase #4 $239.95   6.177%   $254.7717   $254.77   $254.75   $254.80  
  Purchase #5 $180.96   10.283%   $199.5681   $199.57   $199.55   $199.60  
  Purchase #6 $158.96   9.732%   $174.43   $174.43   $174.45   $174.40  
  Purchase #7 $178.43   11.667%   $199.2474   $199.25   $199.25   $199.20  
  7 purchase totals = $1,170.38       $1,268.9274   $1,268.93   $1,268.90   $1,268.90