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 $70.66   9.779%   $77.5698   $77.57   $77.55   $77.60  
  Purchase #2 $107.25   11.589%   $119.6792   $119.68   $119.70   $119.70  
  Purchase #3 $168.87   11.504%   $188.2968   $188.30   $188.30   $188.30  
  Purchase #4 $212.39   12.534%   $239.011   $239.01   $239.00   $239.00  
  Purchase #5 $17.97   12.782%   $20.2669   $20.27   $20.25   $20.30  
  Purchase #6 $163.99   13.857%   $186.7141   $186.71   $186.70   $186.70  
  Purchase #7 $83.91   9.620%   $91.9821   $91.98   $92.00   $92.00  
  7 purchase totals = $825.04       $923.5199   $923.52   $923.50   $923.60