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	$185.70	13.758%	$211.2486	$211.25	$211.25	$211.20
Purchase #2	$138.33	12.610%	$155.7734	$155.77	$155.75	$155.80
Purchase #3	$245.55	3.393%	$253.8815	$253.88	$253.90	$253.90
Purchase #4	$249.31	8.466%	$270.4166	$270.42	$270.40	$270.40
Purchase #5	$113.46	6.566%	$120.9098	$120.91	$120.90	$120.90
Purchase #6	$136.52	11.743%	$152.5515	$152.55	$152.55	$152.60
Purchase #7	$93.95	12.536%	$105.7276	$105.73	$105.75	$105.70
7 purchase totals =	$1,162.82		$1,270.5090	$1,270.51	$1,270.50	$1,270.50