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 $141.87   13.213%   $160.6153   $160.62   $160.60   $160.60  
  Purchase #2 $88.95   4.724%   $93.152   $93.15   $93.15   $93.20  
  Purchase #3 $214.54   10.309%   $236.6569   $236.66   $236.65   $236.70  
  Purchase #4 $43.91   13.724%   $49.9362   $49.94   $49.95   $49.90  
  Purchase #5 $64.29   11.202%   $71.4918   $71.49   $71.50   $71.50  
  Purchase #6 $29.50   6.159%   $31.3169   $31.32   $31.30   $31.30  
  Purchase #7 $183.68   7.813%   $198.0309   $198.03   $198.05   $198.00  
  7 purchase totals = $766.74       $841.2000   $841.21   $841.20   $841.20