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	$51.96	11.214%	$57.7868	$57.79	$57.80	$57.80
Purchase #2	$124.28	4.512%	$129.8875	$129.89	$129.90	$129.90
Purchase #3	$102.43	6.569%	$109.1586	$109.16	$109.15	$109.20
Purchase #4	$231.33	13.507%	$262.5757	$262.58	$262.60	$262.60
Purchase #5	$140.65	12.374%	$158.054	$158.05	$158.05	$158.10
Purchase #6	$84.85	5.669%	$89.6601	$89.66	$89.65	$89.70
Purchase #7	$83.81	3.276%	$86.5556	$86.56	$86.55	$86.60
7 purchase totals =	$819.31		$893.6783	$893.69	$893.70	$893.90