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 $96.25   11.557%   $107.3736   $107.37   $107.35   $107.40  
  Purchase #2 $46.41   6.742%   $49.539   $49.54   $49.55   $49.50  
  Purchase #3 $226.31   5.763%   $239.3522   $239.35   $239.35   $239.40  
  Purchase #4 $169.35   3.806%   $175.7955   $175.80   $175.80   $175.80  
  Purchase #5 $76.61   3.347%   $79.1741   $79.17   $79.15   $79.20  
  Purchase #6 $180.81   11.388%   $201.4006   $201.40   $201.40   $201.40  
  Purchase #7 $180.66   9.427%   $197.6908   $197.69   $197.70   $197.70  
  7 purchase totals = $976.40       $1,050.3258   $1,050.32   $1,050.30   $1,050.40