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	$185.38	3.290%	$191.479	$191.48	$191.50	$191.50
Purchase #2	$180.88	13.867%	$205.9626	$205.96	$205.95	$206.00
Purchase #3	$193.70	7.299%	$207.8382	$207.84	$207.85	$207.80
Purchase #4	$98.59	12.854%	$111.2628	$111.26	$111.25	$111.30
Purchase #5	$104.27	7.336%	$111.9192	$111.92	$111.90	$111.90
Purchase #6	$218.38	12.107%	$244.8193	$244.82	$244.80	$244.80
Purchase #7	$84.54	9.651%	$92.699	$92.70	$92.70	$92.70
7 purchase totals =	$1,065.74		$1,165.9801	$1,165.98	$1,165.95	$1,166.00