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	$82.47	9.438%	$90.2535	$90.25	$90.25	$90.30
Purchase #2	$157.75	9.178%	$172.2283	$172.23	$172.25	$172.20
Purchase #3	$81.48	9.510%	$89.2287	$89.23	$89.25	$89.20
Purchase #4	$188.37	12.158%	$211.272	$211.27	$211.25	$211.30
Purchase #5	$109.46	10.240%	$120.6687	$120.67	$120.65	$120.70
Purchase #6	$89.32	12.290%	$100.2974	$100.30	$100.30	$100.30
Purchase #7	$88.47	9.288%	$96.6871	$96.69	$96.70	$96.70
7 purchase totals =	$797.32		$880.6357	$880.64	$880.65	$880.70