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	$85.72	6.167%	$91.0064	$91.01	$91.00	$91.00
Purchase #2	$72.39	11.441%	$80.6721	$80.67	$80.65	$80.70
Purchase #3	$73.56	6.154%	$78.0869	$78.09	$78.10	$78.10
Purchase #4	$25.37	9.506%	$27.7817	$27.78	$27.80	$27.80
Purchase #5	$145.79	11.493%	$162.5456	$162.55	$162.55	$162.50
Purchase #6	$104.38	13.805%	$118.7897	$118.79	$118.80	$118.80
Purchase #7	$209.75	11.239%	$233.3238	$233.32	$233.30	$233.30
7 purchase totals =	$716.96		$792.2062	$792.21	$792.20	$792.20