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 $112.92   12.123%   $126.6093   $126.61   $126.60   $126.60  
  Purchase #2 $95.87   12.475%   $107.8298   $107.83   $107.85   $107.80  
  Purchase #3 $243.88   12.354%   $274.0089   $274.01   $274.00   $274.00  
  Purchase #4 $131.30   7.412%   $141.032   $141.03   $141.05   $141.00  
  Purchase #5 $115.25   9.796%   $126.5399   $126.54   $126.55   $126.50  
  Purchase #6 $232.60   11.123%   $258.4721   $258.47   $258.45   $258.50  
  Purchase #7 $151.93   11.455%   $169.3336   $169.33   $169.35   $169.30  
  7 purchase totals = $1,083.75       $1,203.8256   $1,203.82   $1,203.85   $1,203.70