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 $215.96   3.352%   $223.199   $223.20   $223.20   $223.20  
  Purchase #2 $45.69   11.203%   $50.8087   $50.81   $50.80   $50.80  
  Purchase #3 $146.26   12.553%   $164.62   $164.62   $164.60   $164.60  
  Purchase #4 $99.40   8.527%   $107.8758   $107.88   $107.90   $107.90  
  Purchase #5 $149.48   9.298%   $163.3787   $163.38   $163.40   $163.40  
  Purchase #6 $103.82   13.656%   $117.9977   $118.00   $118.00   $118.00  
  Purchase #7 $176.96   6.318%   $188.1403   $188.14   $188.15   $188.10  
  7 purchase totals = $937.57       $1,016.0202   $1,016.03   $1,016.05   $1,016.00