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 $204.97   5.124%   $215.4727   $215.47   $215.45   $215.50  
  Purchase #2 $99.33   6.324%   $105.6116   $105.61   $105.60   $105.60  
  Purchase #3 $153.47   3.838%   $159.3602   $159.36   $159.35   $159.40  
  Purchase #4 $215.41   5.294%   $226.8138   $226.81   $226.80   $226.80  
  Purchase #5 $222.91   12.474%   $250.7158   $250.72   $250.70   $250.70  
  Purchase #6 $230.42   8.751%   $250.5841   $250.58   $250.60   $250.60  
  Purchase #7 $230.97   9.816%   $253.642   $253.64   $253.65   $253.60  
  7 purchase totals = $1,357.48       $1,462.2002   $1,462.19   $1,462.15   $1,462.20