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 $194.69   8.852%   $211.924   $211.92   $211.90   $211.90  
  Purchase #2 $145.74   11.161%   $162.006   $162.01   $162.00   $162.00  
  Purchase #3 $154.78   13.699%   $175.9833   $175.98   $176.00   $176.00  
  Purchase #4 $95.43   8.455%   $103.4986   $103.50   $103.50   $103.50  
  Purchase #5 $248.39   8.411%   $269.2821   $269.28   $269.30   $269.30  
  Purchase #6 $80.90   9.453%   $88.5475   $88.55   $88.55   $88.50  
  Purchase #7 $242.39   7.572%   $260.7438   $260.74   $260.75   $260.70  
  7 purchase totals = $1,162.32       $1,271.9853   $1,271.98   $1,272.00   $1,271.90