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 $181.41   13.569%   $206.0255   $206.03   $206.05   $206.00  
  Purchase #2 $197.65   3.645%   $204.8543   $204.85   $204.85   $204.90  
  Purchase #3 $244.44   9.608%   $267.9258   $267.93   $267.95   $267.90  
  Purchase #4 $28.47   3.155%   $29.3682   $29.37   $29.35   $29.40  
  Purchase #5 $221.95   8.746%   $241.3617   $241.36   $241.35   $241.40  
  Purchase #6 $163.68   12.445%   $184.05   $184.05   $184.05   $184.10  
  Purchase #7 $113.76   13.144%   $128.7126   $128.71   $128.70   $128.70  
  7 purchase totals = $1,151.36       $1,262.2981   $1,262.30   $1,262.30   $1,262.40