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	$85.97	6.845%	$91.8546	$91.85	$91.85	$91.90
Purchase #2	$33.38	13.528%	$37.8956	$37.90	$37.90	$37.90
Purchase #3	$115.31	7.459%	$123.911	$123.91	$123.90	$123.90
Purchase #4	$233.95	6.637%	$249.4773	$249.48	$249.50	$249.50
Purchase #5	$86.34	12.457%	$97.0954	$97.10	$97.10	$97.10
Purchase #6	$143.67	6.722%	$153.3275	$153.33	$153.35	$153.30
Purchase #7	$99.53	13.588%	$113.0541	$113.05	$113.05	$113.10
7 purchase totals =	$798.15		$866.6155	$866.62	$866.65	$866.70