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 $198.74   3.745%   $206.1828   $206.18   $206.20   $206.20  
  Purchase #2 $172.31   12.205%   $193.3404   $193.34   $193.35   $193.30  
  Purchase #3 $237.59   5.225%   $250.0041   $250.00   $250.00   $250.00  
  Purchase #4 $218.34   5.368%   $230.0605   $230.06   $230.05   $230.10  
  Purchase #5 $112.55   5.141%   $118.3362   $118.34   $118.35   $118.30  
  Purchase #6 $69.44   4.370%   $72.4745   $72.47   $72.45   $72.50  
  Purchase #7 $32.98   7.641%   $35.5   $35.50   $35.50   $35.50  
  7 purchase totals = $1,041.95       $1,105.8985   $1,105.89   $1,105.90   $1,105.90