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 $103.51   12.699%   $116.6547   $116.65   $116.65   $116.70  
  Purchase #2 $87.50   4.608%   $91.532   $91.53   $91.55   $91.50  
  Purchase #3 $230.75   10.232%   $254.3603   $254.36   $254.35   $254.40  
  Purchase #4 $25.99   12.697%   $29.29   $29.29   $29.30   $29.30  
  Purchase #5 $137.30   12.658%   $154.6794   $154.68   $154.70   $154.70  
  Purchase #6 $68.50   11.273%   $76.222   $76.22   $76.20   $76.20  
  Purchase #7 $223.70   9.193%   $244.2647   $244.26   $244.25   $244.30  
  7 purchase totals = $877.25       $967.0031   $966.99   $967.00   $967.10