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 $246.33   6.198%   $261.5975   $261.60   $261.60   $261.60  
  Purchase #2 $29.67   13.777%   $33.7576   $33.76   $33.75   $33.80  
  Purchase #3 $58.61   12.701%   $66.0541   $66.05   $66.05   $66.10  
  Purchase #4 $224.37   6.482%   $238.9137   $238.91   $238.90   $238.90  
  Purchase #5 $47.65   12.282%   $53.5024   $53.50   $53.50   $53.50  
  Purchase #6 $67.27   10.823%   $74.5506   $74.55   $74.55   $74.60  
  Purchase #7 $61.36   13.644%   $69.732   $69.73   $69.75   $69.70  
  7 purchase totals = $735.26       $798.1079   $798.10   $798.10   $798.20