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 $246.70   5.739%   $260.8581   $260.86   $260.85   $260.90  
  Purchase #2 $52.69   8.181%   $57.0006   $57.00   $57.00   $57.00  
  Purchase #3 $109.37   4.628%   $114.4316   $114.43   $114.45   $114.40  
  Purchase #4 $206.35   8.591%   $224.0775   $224.08   $224.10   $224.10  
  Purchase #5 $75.95   11.668%   $84.8118   $84.81   $84.80   $84.80  
  Purchase #6 $151.46   10.142%   $166.8211   $166.82   $166.80   $166.80  
  Purchase #7 $232.48   9.139%   $253.7263   $253.73   $253.75   $253.70  
  7 purchase totals = $1,075.00       $1,161.7270   $1,161.73   $1,161.75   $1,161.70