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 $230.47   13.610%   $261.837   $261.84   $261.85   $261.80  
  Purchase #2 $132.96   5.313%   $140.0242   $140.02   $140.00   $140.00  
  Purchase #3 $105.53   8.784%   $114.7998   $114.80   $114.80   $114.80  
  Purchase #4 $234.35   7.476%   $251.87   $251.87   $251.85   $251.90  
  Purchase #5 $226.74   12.256%   $254.5293   $254.53   $254.55   $254.50  
  Purchase #6 $221.36   11.242%   $246.2453   $246.25   $246.25   $246.20  
  Purchase #7 $93.46   12.727%   $105.3547   $105.35   $105.35   $105.40  
  7 purchase totals = $1,244.87       $1,374.6603   $1,374.66   $1,374.65   $1,374.60