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	$47.76	3.625%	$49.4913	$49.49	$49.50	$49.50
Purchase #2	$66.82	6.855%	$71.4005	$71.40	$71.40	$71.40
Purchase #3	$36.73	3.869%	$38.1511	$38.15	$38.15	$38.20
Purchase #4	$105.73	3.524%	$109.4559	$109.46	$109.45	$109.50
Purchase #5	$131.59	3.144%	$135.7272	$135.73	$135.75	$135.70
Purchase #6	$37.40	8.226%	$40.4765	$40.48	$40.50	$40.50
Purchase #7	$234.95	8.735%	$255.4729	$255.47	$255.45	$255.50
7 purchase totals =	$660.98		$700.1754	$700.18	$700.20	$700.30