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	$185.67	13.593%	$210.9081	$210.91	$210.90	$210.90
Purchase #2	$170.74	10.486%	$188.6438	$188.64	$188.65	$188.60
Purchase #3	$31.33	13.294%	$35.495	$35.50	$35.50	$35.50
Purchase #4	$243.89	13.807%	$277.5639	$277.56	$277.55	$277.60
Purchase #5	$171.40	4.720%	$179.4901	$179.49	$179.50	$179.50
Purchase #6	$156.28	7.741%	$168.3776	$168.38	$168.40	$168.40
Purchase #7	$231.54	12.769%	$261.1053	$261.11	$261.10	$261.10
7 purchase totals =	$1,190.85		$1,321.5838	$1,321.59	$1,321.60	$1,321.60