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 $218.87   13.283%   $247.9425   $247.94   $247.95   $247.90  
  Purchase #2 $102.87   3.620%   $106.5939   $106.59   $106.60   $106.60  
  Purchase #3 $224.28   13.614%   $254.8135   $254.81   $254.80   $254.80  
  Purchase #4 $235.71   13.805%   $268.2498   $268.25   $268.25   $268.20  
  Purchase #5 $81.63   5.488%   $86.1099   $86.11   $86.10   $86.10  
  Purchase #6 $47.85   9.515%   $52.4029   $52.40   $52.40   $52.40  
  Purchase #7 $181.99   13.614%   $206.7661   $206.77   $206.75   $206.80  
  7 purchase totals = $1,093.20       $1,222.8786   $1,222.87   $1,222.85   $1,222.80