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	$88.32	12.626%	$99.4713	$99.47	$99.45	$99.50
Purchase #2	$101.98	13.687%	$115.938	$115.94	$115.95	$115.90
Purchase #3	$53.96	9.472%	$59.0711	$59.07	$59.05	$59.10
Purchase #4	$60.53	3.661%	$62.746	$62.75	$62.75	$62.70
Purchase #5	$122.88	5.345%	$129.4479	$129.45	$129.45	$129.40
Purchase #6	$120.81	8.874%	$131.5307	$131.53	$131.55	$131.50
Purchase #7	$93.40	12.122%	$104.7219	$104.72	$104.70	$104.70
7 purchase totals =	$641.88		$702.9269	$702.93	$702.90	$702.80