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	$171.51	13.632%	$194.8902	$194.89	$194.90	$194.90
Purchase #2	$72.56	8.426%	$78.6739	$78.67	$78.65	$78.70
Purchase #3	$168.33	7.726%	$181.3352	$181.34	$181.35	$181.30
Purchase #4	$95.84	6.597%	$102.1626	$102.16	$102.15	$102.20
Purchase #5	$29.30	3.810%	$30.4163	$30.42	$30.40	$30.40
Purchase #6	$39.65	10.730%	$43.9044	$43.90	$43.90	$43.90
Purchase #7	$33.41	3.346%	$34.5279	$34.53	$34.55	$34.50
7 purchase totals =	$610.60		$665.9105	$665.91	$665.90	$665.90