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	$137.25	3.658%	$142.2706	$142.27	$142.25	$142.30
Purchase #2	$88.46	8.549%	$96.0224	$96.02	$96.00	$96.00
Purchase #3	$80.48	6.322%	$85.5679	$85.57	$85.55	$85.60
Purchase #4	$157.39	11.363%	$175.2742	$175.27	$175.25	$175.30
Purchase #5	$168.84	10.298%	$186.2271	$186.23	$186.25	$186.20
Purchase #6	$155.47	4.758%	$162.8673	$162.87	$162.85	$162.90
Purchase #7	$129.56	10.671%	$143.3853	$143.39	$143.40	$143.40
7 purchase totals =	$917.45		$991.6148	$991.62	$991.55	$991.70