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	$175.43	13.167%	$198.5289	$198.53	$198.55	$198.50
Purchase #2	$241.40	10.568%	$266.9112	$266.91	$266.90	$266.90
Purchase #3	$186.28	12.291%	$209.1757	$209.18	$209.20	$209.20
Purchase #4	$140.41	8.411%	$152.2199	$152.22	$152.20	$152.20
Purchase #5	$12.33	12.708%	$13.8969	$13.90	$13.90	$13.90
Purchase #6	$237.34	7.516%	$255.1785	$255.18	$255.20	$255.20
Purchase #7	$42.97	4.821%	$45.0416	$45.04	$45.05	$45.00
7 purchase totals =	$1,036.16		$1,140.9527	$1,140.96	$1,141.00	$1,140.90