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	$73.61	12.119%	$82.5308	$82.53	$82.55	$82.50
Purchase #2	$219.59	7.722%	$236.5467	$236.55	$236.55	$236.50
Purchase #3	$191.81	4.263%	$199.9869	$199.99	$200.00	$200.00
Purchase #4	$39.99	6.860%	$42.7333	$42.73	$42.75	$42.70
Purchase #5	$96.29	3.476%	$99.637	$99.64	$99.65	$99.60
Purchase #6	$29.61	9.199%	$32.3338	$32.33	$32.35	$32.30
Purchase #7	$118.82	6.698%	$126.7786	$126.78	$126.80	$126.80
7 purchase totals =	$769.72		$820.5471	$820.55	$820.65	$820.40