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 $67.86   12.284%   $76.1959   $76.20   $76.20   $76.20  
  Purchase #2 $212.47   8.514%   $230.5597   $230.56   $230.55   $230.60  
  Purchase #3 $46.46   13.566%   $52.7628   $52.76   $52.75   $52.80  
  Purchase #4 $130.97   12.145%   $146.8763   $146.88   $146.90   $146.90  
  Purchase #5 $115.66   4.508%   $120.874   $120.87   $120.85   $120.90  
  Purchase #6 $135.32   4.202%   $141.0061   $141.01   $141.00   $141.00  
  Purchase #7 $73.83   3.553%   $76.4532   $76.45   $76.45   $76.50  
  7 purchase totals = $782.57       $844.7280   $844.73   $844.70   $844.90