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 $99.60   7.850%   $107.4186   $107.42   $107.40   $107.40  
  Purchase #2 $113.30   9.699%   $124.289   $124.29   $124.30   $124.30  
  Purchase #3 $151.87   9.848%   $166.8262   $166.83   $166.85   $166.80  
  Purchase #4 $172.66   10.723%   $191.1743   $191.17   $191.15   $191.20  
  Purchase #5 $123.40   10.128%   $135.898   $135.90   $135.90   $135.90  
  Purchase #6 $216.27   8.268%   $234.1512   $234.15   $234.15   $234.20  
  Purchase #7 $245.82   13.777%   $279.6866   $279.69   $279.70   $279.70  
  7 purchase totals = $1,122.92       $1,239.4439   $1,239.45   $1,239.45   $1,239.50