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 $201.78   11.686%   $225.36   $225.36   $225.35   $225.40  
  Purchase #2 $231.30   11.817%   $258.6327   $258.63   $258.65   $258.60  
  Purchase #3 $50.89   3.616%   $52.7302   $52.73   $52.75   $52.70  
  Purchase #4 $158.53   5.806%   $167.7343   $167.73   $167.75   $167.70  
  Purchase #5 $196.61   10.693%   $217.6335   $217.63   $217.65   $217.60  
  Purchase #6 $183.97   5.444%   $193.9853   $193.99   $194.00   $194.00  
  Purchase #7 $20.70   13.588%   $23.5127   $23.51   $23.50   $23.50  
  7 purchase totals = $1,043.78       $1,139.5887   $1,139.58   $1,139.65   $1,139.50