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	$24.56	11.316%	$27.3392	$27.34	$27.35	$27.30
Purchase #2	$37.62	6.115%	$39.9205	$39.92	$39.90	$39.90
Purchase #3	$208.31	4.330%	$217.3298	$217.33	$217.35	$217.30
Purchase #4	$96.50	7.706%	$103.9363	$103.94	$103.95	$103.90
Purchase #5	$179.49	3.465%	$185.7093	$185.71	$185.70	$185.70
Purchase #6	$80.45	12.862%	$90.7975	$90.80	$90.80	$90.80
Purchase #7	$75.37	7.287%	$80.8622	$80.86	$80.85	$80.90
7 purchase totals =	$702.30		$745.8948	$745.90	$745.90	$745.80