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 $60.88   5.173%   $64.0293   $64.03   $64.05   $64.00  
  Purchase #2 $161.87   12.469%   $182.0536   $182.05   $182.05   $182.10  
  Purchase #3 $61.26   13.430%   $69.4872   $69.49   $69.50   $69.50  
  Purchase #4 $30.59   9.269%   $33.4254   $33.43   $33.45   $33.40  
  Purchase #5 $120.48   8.172%   $130.3256   $130.33   $130.35   $130.30  
  Purchase #6 $199.58   12.753%   $225.0324   $225.03   $225.05   $225.00  
  Purchase #7 $17.26   9.858%   $18.9615   $18.96   $18.95   $19.00  
  7 purchase totals = $651.92       $723.3150   $723.32   $723.40   $723.30