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	$44.78	11.552%	$49.953	$49.95	$49.95	$50.00
Purchase #2	$79.51	7.475%	$85.4534	$85.45	$85.45	$85.50
Purchase #3	$233.72	4.229%	$243.604	$243.60	$243.60	$243.60
Purchase #4	$114.57	3.873%	$119.0073	$119.01	$119.00	$119.00
Purchase #5	$45.91	5.732%	$48.5416	$48.54	$48.55	$48.50
Purchase #6	$179.62	4.655%	$187.9813	$187.98	$188.00	$188.00
Purchase #7	$55.27	7.503%	$59.4169	$59.42	$59.40	$59.40
7 purchase totals =	$753.38		$793.9575	$793.95	$793.95	$794.00