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 $195.53   6.310%   $207.8679   $207.87   $207.85   $207.90  
  Purchase #2 $58.92   6.226%   $62.5884   $62.59   $62.60   $62.60  
  Purchase #3 $200.72   6.771%   $214.3108   $214.31   $214.30   $214.30  
  Purchase #4 $100.63   3.863%   $104.5173   $104.52   $104.50   $104.50  
  Purchase #5 $35.61   8.653%   $38.6913   $38.69   $38.70   $38.70  
  Purchase #6 $209.67   9.112%   $228.7751   $228.78   $228.80   $228.80  
  Purchase #7 $150.90   9.233%   $164.8326   $164.83   $164.85   $164.80  
  7 purchase totals = $951.98       $1,021.5834   $1,021.59   $1,021.60   $1,021.60