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	$170.92	11.806%	$191.0988	$191.10	$191.10	$191.10
Purchase #2	$45.86	5.570%	$48.4144	$48.41	$48.40	$48.40
Purchase #3	$113.27	12.759%	$127.7221	$127.72	$127.70	$127.70
Purchase #4	$63.67	5.288%	$67.0369	$67.04	$67.05	$67.00
Purchase #5	$200.44	4.744%	$209.9489	$209.95	$209.95	$209.90
Purchase #6	$25.69	12.513%	$28.9046	$28.90	$28.90	$28.90
Purchase #7	$227.57	10.577%	$251.6401	$251.64	$251.65	$251.60
7 purchase totals =	$847.42		$924.7658	$924.76	$924.75	$924.60