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 $45.66   5.204%   $48.0361   $48.04   $48.05   $48.00  
  Purchase #2 $122.31   13.566%   $138.9026   $138.90   $138.90   $138.90  
  Purchase #3 $214.89   5.181%   $226.0235   $226.02   $226.00   $226.00  
  Purchase #4 $69.57   5.591%   $73.4597   $73.46   $73.45   $73.50  
  Purchase #5 $174.76   6.579%   $186.2575   $186.26   $186.25   $186.30  
  Purchase #6 $47.65   4.602%   $49.8429   $49.84   $49.85   $49.80  
  Purchase #7 $37.38   6.609%   $39.8504   $39.85   $39.85   $39.90  
  7 purchase totals = $712.22       $762.3727   $762.37   $762.35   $762.40