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 $67.35   6.305%   $71.5964   $71.60   $71.60   $71.60  
  Purchase #2 $205.40   9.692%   $225.3074   $225.31   $225.30   $225.30  
  Purchase #3 $241.43   10.423%   $266.5942   $266.59   $266.60   $266.60  
  Purchase #4 $107.61   10.256%   $118.6465   $118.65   $118.65   $118.60  
  Purchase #5 $231.70   12.513%   $260.6926   $260.69   $260.70   $260.70  
  Purchase #6 $233.78   5.161%   $245.8454   $245.85   $245.85   $245.80  
  Purchase #7 $56.97   6.803%   $60.8457   $60.85   $60.85   $60.80  
  7 purchase totals = $1,144.24       $1,249.5282   $1,249.54   $1,249.55   $1,249.40