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 $192.41   12.695%   $216.8364   $216.84   $216.85   $216.80  
  Purchase #2 $250.90   7.552%   $269.848   $269.85   $269.85   $269.80  
  Purchase #3 $202.37   13.584%   $229.8599   $229.86   $229.85   $229.90  
  Purchase #4 $159.33   12.385%   $179.063   $179.06   $179.05   $179.10  
  Purchase #5 $72.38   12.265%   $81.2574   $81.26   $81.25   $81.30  
  Purchase #6 $152.43   6.260%   $161.9721   $161.97   $161.95   $162.00  
  Purchase #7 $241.79   12.177%   $271.2328   $271.23   $271.25   $271.20  
  7 purchase totals = $1,271.61       $1,410.0696   $1,410.07   $1,410.05   $1,410.10