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 $115.74   8.295%   $125.3406   $125.34   $125.35   $125.30  
  Purchase #2 $239.83   13.729%   $272.7563   $272.76   $272.75   $272.80  
  Purchase #3 $70.70   6.564%   $75.3407   $75.34   $75.35   $75.30  
  Purchase #4 $248.85   4.190%   $259.2768   $259.28   $259.30   $259.30  
  Purchase #5 $152.32   9.262%   $166.4279   $166.43   $166.45   $166.40  
  Purchase #6 $241.80   13.353%   $274.0876   $274.09   $274.10   $274.10  
  Purchase #7 $54.64   13.477%   $62.0038   $62.00   $62.00   $62.00  
  7 purchase totals = $1,123.88       $1,235.2337   $1,235.24   $1,235.30   $1,235.20