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	$33.72	10.868%	$37.3847	$37.38	$37.40	$37.40
Purchase #2	$93.98	4.406%	$98.1208	$98.12	$98.10	$98.10
Purchase #3	$127.55	6.774%	$136.1902	$136.19	$136.20	$136.20
Purchase #4	$85.59	7.605%	$92.0991	$92.10	$92.10	$92.10
Purchase #5	$243.91	6.376%	$259.4617	$259.46	$259.45	$259.50
Purchase #6	$148.90	11.411%	$165.891	$165.89	$165.90	$165.90
Purchase #7	$47.43	10.495%	$52.4078	$52.41	$52.40	$52.40
7 purchase totals =	$781.08		$841.5553	$841.55	$841.55	$841.60