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	$38.35	9.110%	$41.8437	$41.84	$41.85	$41.80
Purchase #2	$21.41	4.860%	$22.4505	$22.45	$22.45	$22.50
Purchase #3	$133.72	4.344%	$139.5288	$139.53	$139.55	$139.50
Purchase #4	$233.72	12.735%	$263.4842	$263.48	$263.50	$263.50
Purchase #5	$215.36	10.286%	$237.5119	$237.51	$237.50	$237.50
Purchase #6	$230.69	13.228%	$261.2057	$261.21	$261.20	$261.20
Purchase #7	$33.35	11.859%	$37.305	$37.31	$37.30	$37.30
7 purchase totals =	$906.60		$1,003.3298	$1,003.33	$1,003.35	$1,003.30