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 $65.77   6.796%   $70.2397   $70.24   $70.25   $70.20  
  Purchase #2 $118.45   10.393%   $130.7605   $130.76   $130.75   $130.80  
  Purchase #3 $118.71   12.446%   $133.4846   $133.48   $133.50   $133.50  
  Purchase #4 $236.60   7.374%   $254.0469   $254.05   $254.05   $254.00  
  Purchase #5 $43.73   9.775%   $48.0046   $48.00   $48.00   $48.00  
  Purchase #6 $190.55   5.693%   $201.398   $201.40   $201.40   $201.40  
  Purchase #7 $90.28   7.127%   $96.7143   $96.71   $96.70   $96.70  
  7 purchase totals = $864.09       $934.6486   $934.64   $934.65   $934.60