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 $183.34   12.362%   $206.0045   $206.00   $206.00   $206.00  
  Purchase #2 $148.36   9.737%   $162.8058   $162.81   $162.80   $162.80  
  Purchase #3 $5.80   5.710%   $6.1312   $6.13   $6.15   $6.10  
  Purchase #4 $29.54   5.721%   $31.23   $31.23   $31.25   $31.20  
  Purchase #5 $169.74   9.354%   $185.6175   $185.62   $185.60   $185.60  
  Purchase #6 $211.62   3.218%   $218.4299   $218.43   $218.45   $218.40  
  Purchase #7 $196.26   8.705%   $213.3444   $213.34   $213.35   $213.30  
  7 purchase totals = $944.66       $1,023.5633   $1,023.56   $1,023.60   $1,023.40