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 $56.32   8.659%   $61.1967   $61.20   $61.20   $61.20  
  Purchase #2 $58.44   12.597%   $65.8017   $65.80   $65.80   $65.80  
  Purchase #3 $240.72   13.429%   $273.0463   $273.05   $273.05   $273.00  
  Purchase #4 $165.39   10.393%   $182.579   $182.58   $182.60   $182.60  
  Purchase #5 $54.75   12.741%   $61.7257   $61.73   $61.75   $61.70  
  Purchase #6 $135.56   8.532%   $147.126   $147.13   $147.15   $147.10  
  Purchase #7 $227.82   4.665%   $238.4478   $238.45   $238.45   $238.40  
  7 purchase totals = $939.00       $1,029.9232   $1,029.94   $1,030.00   $1,029.80