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	$175.74	7.552%	$189.0119	$189.01	$189.00	$189.00
Purchase #2	$202.81	5.118%	$213.1898	$213.19	$213.20	$213.20
Purchase #3	$133.74	4.375%	$139.5911	$139.59	$139.60	$139.60
Purchase #4	$166.56	10.121%	$183.4175	$183.42	$183.40	$183.40
Purchase #5	$56.33	5.135%	$59.2225	$59.22	$59.20	$59.20
Purchase #6	$182.89	4.133%	$190.4488	$190.45	$190.45	$190.40
Purchase #7	$239.57	3.234%	$247.3177	$247.32	$247.30	$247.30
7 purchase totals =	$1,157.64		$1,222.1993	$1,222.20	$1,222.15	$1,222.10