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	$91.38	7.801%	$98.5086	$98.51	$98.50	$98.50
Purchase #2	$225.27	6.335%	$239.5409	$239.54	$239.55	$239.50
Purchase #3	$165.39	9.329%	$180.8192	$180.82	$180.80	$180.80
Purchase #4	$247.91	11.238%	$275.7701	$275.77	$275.75	$275.80
Purchase #5	$127.45	10.486%	$140.8144	$140.81	$140.80	$140.80
Purchase #6	$165.25	4.646%	$172.9275	$172.93	$172.95	$172.90
Purchase #7	$156.67	9.179%	$171.0507	$171.05	$171.05	$171.10
7 purchase totals =	$1,179.32		$1,279.4314	$1,279.43	$1,279.40	$1,279.40