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	$112.30	6.337%	$119.4165	$119.42	$119.40	$119.40
Purchase #2	$210.44	6.116%	$223.3105	$223.31	$223.30	$223.30
Purchase #3	$168.64	6.843%	$180.18	$180.18	$180.20	$180.20
Purchase #4	$77.67	6.499%	$82.7178	$82.72	$82.70	$82.70
Purchase #5	$134.74	5.559%	$142.2302	$142.23	$142.25	$142.20
Purchase #6	$75.33	3.708%	$78.1232	$78.12	$78.10	$78.10
Purchase #7	$105.39	4.631%	$110.2706	$110.27	$110.25	$110.30
7 purchase totals =	$884.51		$936.2488	$936.25	$936.20	$936.20