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	$81.89	11.790%	$91.5448	$91.54	$91.55	$91.50
Purchase #2	$38.77	8.851%	$42.2015	$42.20	$42.20	$42.20
Purchase #3	$134.92	11.419%	$150.3265	$150.33	$150.35	$150.30
Purchase #4	$58.34	10.518%	$64.4762	$64.48	$64.50	$64.50
Purchase #5	$168.32	3.452%	$174.1304	$174.13	$174.15	$174.10
Purchase #6	$48.28	12.353%	$54.244	$54.24	$54.25	$54.20
Purchase #7	$108.35	3.560%	$112.2073	$112.21	$112.20	$112.20
7 purchase totals =	$638.87		$689.1307	$689.13	$689.20	$689.00