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 $226.65   13.676%   $257.6467   $257.65   $257.65   $257.60  
  Purchase #2 $217.64   10.542%   $240.5836   $240.58   $240.60   $240.60  
  Purchase #3 $57.98   6.784%   $61.9134   $61.91   $61.90   $61.90  
  Purchase #4 $108.83   5.814%   $115.1574   $115.16   $115.15   $115.20  
  Purchase #5 $216.91   12.805%   $244.6853   $244.69   $244.70   $244.70  
  Purchase #6 $207.69   8.533%   $225.4122   $225.41   $225.40   $225.40  
  Purchase #7 $168.36   11.601%   $187.8914   $187.89   $187.90   $187.90  
  7 purchase totals = $1,204.06       $1,333.2900   $1,333.29   $1,333.30   $1,333.30