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 $10.85   11.652%   $12.1142   $12.11   $12.10   $12.10  
  Purchase #2 $163.83   13.532%   $185.9995   $186.00   $186.00   $186.00  
  Purchase #3 $69.52   3.571%   $72.0026   $72.00   $72.00   $72.00  
  Purchase #4 $207.28   6.584%   $220.9273   $220.93   $220.95   $220.90  
  Purchase #5 $55.39   10.286%   $61.0874   $61.09   $61.10   $61.10  
  Purchase #6 $212.60   4.507%   $222.1819   $222.18   $222.20   $222.20  
  Purchase #7 $15.89   4.833%   $16.658   $16.66   $16.65   $16.70  
  7 purchase totals = $735.36       $790.9709   $790.97   $791.00   $791.00