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 $68.55   7.411%   $73.6302   $73.63   $73.65   $73.60  
  Purchase #2 $41.30   5.351%   $43.51   $43.51   $43.50   $43.50  
  Purchase #3 $232.25   8.757%   $252.5881   $252.59   $252.60   $252.60  
  Purchase #4 $16.72   5.835%   $17.6956   $17.70   $17.70   $17.70  
  Purchase #5 $192.79   4.334%   $201.1455   $201.15   $201.15   $201.10  
  Purchase #6 $131.54   8.423%   $142.6196   $142.62   $142.60   $142.60  
  Purchase #7 $248.40   13.361%   $281.5887   $281.59   $281.60   $281.60  
  7 purchase totals = $931.55       $1,012.7777   $1,012.79   $1,012.80   $1,012.70