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 $218.77   10.333%   $241.3755   $241.38   $241.40   $241.40  
  Purchase #2 $121.56   7.239%   $130.3597   $130.36   $130.35   $130.40  
  Purchase #3 $204.86   5.563%   $216.2564   $216.26   $216.25   $216.30  
  Purchase #4 $182.34   13.445%   $206.8556   $206.86   $206.85   $206.90  
  Purchase #5 $127.71   5.809%   $135.1287   $135.13   $135.15   $135.10  
  Purchase #6 $51.95   7.747%   $55.9746   $55.97   $55.95   $56.00  
  Purchase #7 $69.64   4.434%   $72.7278   $72.73   $72.75   $72.70  
  7 purchase totals = $976.83       $1,058.6783   $1,058.69   $1,058.70   $1,058.80