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	$79.83	8.759%	$86.8223	$86.82	$86.80	$86.80
Purchase #2	$142.54	8.144%	$154.1485	$154.15	$154.15	$154.10
Purchase #3	$193.48	8.347%	$209.6298	$209.63	$209.65	$209.60
Purchase #4	$30.54	12.597%	$34.3871	$34.39	$34.40	$34.40
Purchase #5	$70.46	11.443%	$78.5227	$78.52	$78.50	$78.50
Purchase #6	$40.45	4.227%	$42.1598	$42.16	$42.15	$42.20
Purchase #7	$165.39	6.107%	$175.4904	$175.49	$175.50	$175.50
7 purchase totals =	$722.69		$781.1606	$781.16	$781.15	$781.10