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	$52.92	7.545%	$56.9128	$56.91	$56.90	$56.90
Purchase #2	$102.37	7.164%	$109.7038	$109.70	$109.70	$109.70
Purchase #3	$64.31	4.481%	$67.1917	$67.19	$67.20	$67.20
Purchase #4	$242.85	3.132%	$250.4561	$250.46	$250.45	$250.50
Purchase #5	$81.40	5.820%	$86.1375	$86.14	$86.15	$86.10
Purchase #6	$103.83	4.612%	$108.6186	$108.62	$108.60	$108.60
Purchase #7	$131.48	12.166%	$147.4759	$147.48	$147.50	$147.50
7 purchase totals =	$779.16		$826.4964	$826.50	$826.50	$826.50