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 $68.45   11.605%   $76.3936   $76.39   $76.40   $76.40  
  Purchase #2 $158.33   10.613%   $175.1336   $175.13   $175.15   $175.10  
  Purchase #3 $199.34   8.405%   $216.0945   $216.09   $216.10   $216.10  
  Purchase #4 $235.35   6.270%   $250.1064   $250.11   $250.10   $250.10  
  Purchase #5 $211.45   12.750%   $238.4099   $238.41   $238.40   $238.40  
  Purchase #6 $32.92   8.379%   $35.6784   $35.68   $35.70   $35.70  
  Purchase #7 $90.82   8.784%   $98.7976   $98.80   $98.80   $98.80  
  7 purchase totals = $996.66       $1,090.6140   $1,090.61   $1,090.65   $1,090.60