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 $215.46   11.477%   $240.1883   $240.19   $240.20   $240.20  
  Purchase #2 $185.56   3.471%   $192.0008   $192.00   $192.00   $192.00  
  Purchase #3 $52.65   9.514%   $57.6591   $57.66   $57.65   $57.70  
  Purchase #4 $174.83   5.173%   $183.874   $183.87   $183.85   $183.90  
  Purchase #5 $221.89   13.322%   $251.4502   $251.45   $251.45   $251.50  
  Purchase #6 $185.46   13.778%   $211.0127   $211.01   $211.00   $211.00  
  Purchase #7 $57.71   6.616%   $61.5281   $61.53   $61.55   $61.50  
  7 purchase totals = $1,093.56       $1,197.7132   $1,197.71   $1,197.70   $1,197.80