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 $208.28   13.221%   $235.8167   $235.82   $235.80   $235.80  
  Purchase #2 $116.92   5.322%   $123.1425   $123.14   $123.15   $123.10  
  Purchase #3 $35.96   4.670%   $37.6393   $37.64   $37.65   $37.60  
  Purchase #4 $208.54   10.418%   $230.2657   $230.27   $230.25   $230.30  
  Purchase #5 $211.67   12.232%   $237.5615   $237.56   $237.55   $237.60  
  Purchase #6 $175.43   4.538%   $183.391   $183.39   $183.40   $183.40  
  Purchase #7 $153.42   4.215%   $159.8867   $159.89   $159.90   $159.90  
  7 purchase totals = $1,110.22       $1,207.7034   $1,207.71   $1,207.70   $1,207.70