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 $50.26   13.517%   $57.0536   $57.05   $57.05   $57.10  
  Purchase #2 $217.48   12.114%   $243.8255   $243.83   $243.85   $243.80  
  Purchase #3 $69.44   4.763%   $72.7474   $72.75   $72.75   $72.70  
  Purchase #4 $160.94   11.445%   $179.3596   $179.36   $179.35   $179.40  
  Purchase #5 $23.60   12.618%   $26.5778   $26.58   $26.60   $26.60  
  Purchase #6 $168.43   4.616%   $176.2047   $176.20   $176.20   $176.20  
  Purchase #7 $18.91   10.802%   $20.9527   $20.95   $20.95   $21.00  
  7 purchase totals = $709.06       $776.7213   $776.72   $776.75   $776.80