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 $244.41   9.166%   $266.8126   $266.81   $266.80   $266.80  
  Purchase #2 $215.77   4.654%   $225.8119   $225.81   $225.80   $225.80  
  Purchase #3 $55.50   11.158%   $61.6927   $61.69   $61.70   $61.70  
  Purchase #4 $239.85   7.153%   $257.0065   $257.01   $257.00   $257.00  
  Purchase #5 $127.81   9.740%   $140.2587   $140.26   $140.25   $140.30  
  Purchase #6 $65.35   4.864%   $68.5286   $68.53   $68.55   $68.50  
  Purchase #7 $93.66   7.640%   $100.8156   $100.82   $100.80   $100.80  
  7 purchase totals = $1,042.35       $1,120.9266   $1,120.93   $1,120.90   $1,120.90