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 $74.37   5.565%   $78.5087   $78.51   $78.50   $78.50  
  Purchase #2 $206.40   4.683%   $216.0657   $216.07   $216.05   $216.10  
  Purchase #3 $179.62   13.300%   $203.5095   $203.51   $203.50   $203.50  
  Purchase #4 $111.29   12.487%   $125.1868   $125.19   $125.20   $125.20  
  Purchase #5 $192.94   10.789%   $213.7563   $213.76   $213.75   $213.80  
  Purchase #6 $89.55   4.183%   $93.2959   $93.30   $93.30   $93.30  
  Purchase #7 $88.99   7.831%   $95.9588   $95.96   $95.95   $96.00  
  7 purchase totals = $943.16       $1,026.2817   $1,026.30   $1,026.25   $1,026.40