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 $61.95   8.632%   $67.2975   $67.30   $67.30   $67.30  
  Purchase #2 $160.34   7.330%   $172.0929   $172.09   $172.10   $172.10  
  Purchase #3 $31.41   8.395%   $34.0469   $34.05   $34.05   $34.00  
  Purchase #4 $214.73   4.790%   $225.0156   $225.02   $225.00   $225.00  
  Purchase #5 $171.79   4.733%   $179.9208   $179.92   $179.90   $179.90  
  Purchase #6 $212.81   13.644%   $241.8458   $241.85   $241.85   $241.80  
  Purchase #7 $46.75   7.376%   $50.1983   $50.20   $50.20   $50.20  
  7 purchase totals = $899.78       $970.4178   $970.43   $970.40   $970.30