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 $138.34   9.691%   $151.7465   $151.75   $151.75   $151.70  
  Purchase #2 $240.51   10.833%   $266.5644   $266.56   $266.55   $266.60  
  Purchase #3 $201.68   9.592%   $221.0251   $221.03   $221.05   $221.00  
  Purchase #4 $196.70   10.205%   $216.7732   $216.77   $216.75   $216.80  
  Purchase #5 $91.30   13.453%   $103.5826   $103.58   $103.60   $103.60  
  Purchase #6 $127.78   10.565%   $141.28   $141.28   $141.30   $141.30  
  Purchase #7 $58.89   8.793%   $64.0682   $64.07   $64.05   $64.10  
  7 purchase totals = $1,055.20       $1,165.0400   $1,165.04   $1,165.05   $1,165.10