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	$80.87	5.705%	$85.4836	$85.48	$85.50	$85.50
Purchase #2	$191.75	11.102%	$213.0381	$213.04	$213.05	$213.00
Purchase #3	$247.42	5.364%	$260.6916	$260.69	$260.70	$260.70
Purchase #4	$129.47	9.316%	$141.5314	$141.53	$141.55	$141.50
Purchase #5	$224.64	6.819%	$239.9582	$239.96	$239.95	$240.00
Purchase #6	$86.85	4.707%	$90.938	$90.94	$90.95	$90.90
Purchase #7	$241.55	11.206%	$268.6181	$268.62	$268.60	$268.60
7 purchase totals =	$1,202.55		$1,300.2590	$1,300.26	$1,300.30	$1,300.20