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	$245.35	12.133%	$275.1183	$275.12	$275.10	$275.10
Purchase #2	$16.36	8.394%	$17.7333	$17.73	$17.75	$17.70
Purchase #3	$182.57	9.854%	$200.5604	$200.56	$200.55	$200.60
Purchase #4	$86.33	7.574%	$92.8686	$92.87	$92.85	$92.90
Purchase #5	$93.73	5.740%	$99.1101	$99.11	$99.10	$99.10
Purchase #6	$27.36	3.745%	$28.3846	$28.38	$28.40	$28.40
Purchase #7	$77.37	6.646%	$82.512	$82.51	$82.50	$82.50
7 purchase totals =	$729.07		$796.2873	$796.28	$796.25	$796.30