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 $112.73   10.492%   $124.5576   $124.56   $124.55   $124.60  
  Purchase #2 $123.99   6.358%   $131.8733   $131.87   $131.85   $131.90  
  Purchase #3 $99.82   13.166%   $112.9623   $112.96   $112.95   $113.00  
  Purchase #4 $146.58   6.606%   $156.2631   $156.26   $156.25   $156.30  
  Purchase #5 $50.33   6.668%   $53.686   $53.69   $53.70   $53.70  
  Purchase #6 $119.32   6.193%   $126.7095   $126.71   $126.70   $126.70  
  Purchase #7 $226.98   7.418%   $243.8174   $243.82   $243.80   $243.80  
  7 purchase totals = $879.75       $949.8692   $949.87   $949.80   $950.00