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 $108.76   5.261%   $114.4819   $114.48   $114.50   $114.50  
  Purchase #2 $141.38   8.316%   $153.1372   $153.14   $153.15   $153.10  
  Purchase #3 $108.35   11.198%   $120.483   $120.48   $120.50   $120.50  
  Purchase #4 $167.28   8.748%   $181.9137   $181.91   $181.90   $181.90  
  Purchase #5 $218.36   6.658%   $232.8984   $232.90   $232.90   $232.90  
  Purchase #6 $183.90   10.476%   $203.1654   $203.17   $203.15   $203.20  
  Purchase #7 $65.27   10.708%   $72.2591   $72.26   $72.25   $72.30  
  7 purchase totals = $993.30       $1,078.3387   $1,078.34   $1,078.35   $1,078.40