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	$98.79	5.407%	$104.1316	$104.13	$104.15	$104.10
Purchase #2	$187.83	12.391%	$211.104	$211.10	$211.10	$211.10
Purchase #3	$42.47	7.470%	$45.6425	$45.64	$45.65	$45.60
Purchase #4	$73.61	7.346%	$79.0174	$79.02	$79.00	$79.00
Purchase #5	$183.79	7.131%	$196.8961	$196.90	$196.90	$196.90
Purchase #6	$143.67	3.518%	$148.7243	$148.72	$148.70	$148.70
Purchase #7	$107.33	13.506%	$121.826	$121.83	$121.85	$121.80
7 purchase totals =	$837.49		$907.3419	$907.34	$907.35	$907.20