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 $55.95   4.719%   $58.5903   $58.59   $58.60   $58.60  
  Purchase #2 $27.93   6.155%   $29.6491   $29.65   $29.65   $29.60  
  Purchase #3 $20.60   9.365%   $22.5292   $22.53   $22.55   $22.50  
  Purchase #4 $236.49   3.860%   $245.6185   $245.62   $245.60   $245.60  
  Purchase #5 $54.98   8.290%   $59.5378   $59.54   $59.55   $59.50  
  Purchase #6 $129.69   7.848%   $139.8681   $139.87   $139.85   $139.90  
  Purchase #7 $162.54   8.858%   $176.9378   $176.94   $176.95   $176.90  
  7 purchase totals = $688.18       $732.7308   $732.74   $732.75   $732.60