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 $142.53   6.368%   $151.6063   $151.61   $151.60   $151.60  
  Purchase #2 $93.90   11.628%   $104.8187   $104.82   $104.80   $104.80  
  Purchase #3 $33.59   7.678%   $36.169   $36.17   $36.15   $36.20  
  Purchase #4 $56.96   5.611%   $60.156   $60.16   $60.15   $60.20  
  Purchase #5 $135.47   5.857%   $143.4045   $143.40   $143.40   $143.40  
  Purchase #6 $99.42   7.103%   $106.4818   $106.48   $106.50   $106.50  
  Purchase #7 $206.47   12.469%   $232.2147   $232.21   $232.20   $232.20  
  7 purchase totals = $768.34       $834.8510   $834.85   $834.80   $834.90