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 $199.78   3.731%   $207.2338   $207.23   $207.25   $207.20  
  Purchase #2 $152.33   9.219%   $166.3733   $166.37   $166.35   $166.40  
  Purchase #3 $156.60   4.671%   $163.9148   $163.91   $163.90   $163.90  
  Purchase #4 $66.62   4.586%   $69.6752   $69.68   $69.70   $69.70  
  Purchase #5 $80.82   12.165%   $90.6518   $90.65   $90.65   $90.70  
  Purchase #6 $190.61   12.701%   $214.8194   $214.82   $214.80   $214.80  
  Purchase #7 $110.73   8.745%   $120.4133   $120.41   $120.40   $120.40  
  7 purchase totals = $957.49       $1,033.0816   $1,033.07   $1,033.05   $1,033.10