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	$245.38	12.333%	$275.6427	$275.64	$275.65	$275.60
Purchase #2	$187.32	4.768%	$196.2514	$196.25	$196.25	$196.30
Purchase #3	$192.70	10.665%	$213.2515	$213.25	$213.25	$213.30
Purchase #4	$171.33	9.481%	$187.5738	$187.57	$187.55	$187.60
Purchase #5	$135.49	3.264%	$139.9124	$139.91	$139.90	$139.90
Purchase #6	$56.41	4.332%	$58.8537	$58.85	$58.85	$58.90
Purchase #7	$119.95	7.629%	$129.101	$129.10	$129.10	$129.10
7 purchase totals =	$1,108.58		$1,200.5865	$1,200.57	$1,200.55	$1,200.70