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 $159.26   4.377%   $166.2308   $166.23   $166.25   $166.20  
  Purchase #2 $187.68   10.408%   $207.2137   $207.21   $207.20   $207.20  
  Purchase #3 $199.97   7.459%   $214.8858   $214.89   $214.90   $214.90  
  Purchase #4 $109.77   11.560%   $122.4594   $122.46   $122.45   $122.50  
  Purchase #5 $39.58   8.708%   $43.0266   $43.03   $43.05   $43.00  
  Purchase #6 $136.85   8.240%   $148.1264   $148.13   $148.15   $148.10  
  Purchase #7 $116.42   12.168%   $130.586   $130.59   $130.60   $130.60  
  7 purchase totals = $949.53       $1,032.5287   $1,032.54   $1,032.60   $1,032.50