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	$197.44	6.121%	$209.5253	$209.53	$209.55	$209.50
Purchase #2	$97.70	7.786%	$105.3069	$105.31	$105.30	$105.30
Purchase #3	$175.25	9.327%	$191.5956	$191.60	$191.60	$191.60
Purchase #4	$99.59	5.545%	$105.1123	$105.11	$105.10	$105.10
Purchase #5	$175.27	13.477%	$198.8911	$198.89	$198.90	$198.90
Purchase #6	$90.74	8.107%	$98.0963	$98.10	$98.10	$98.10
Purchase #7	$69.61	9.655%	$76.3308	$76.33	$76.35	$76.30
7 purchase totals =	$905.60		$984.8583	$984.87	$984.90	$984.80