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	$179.92	3.872%	$186.8865	$186.89	$186.90	$186.90
Purchase #2	$250.96	10.632%	$277.6421	$277.64	$277.65	$277.60
Purchase #3	$228.39	9.677%	$250.4913	$250.49	$250.50	$250.50
Purchase #4	$215.70	12.158%	$241.9248	$241.92	$241.90	$241.90
Purchase #5	$55.80	12.619%	$62.8414	$62.84	$62.85	$62.80
Purchase #6	$185.35	11.562%	$206.7802	$206.78	$206.80	$206.80
Purchase #7	$189.97	3.247%	$196.1383	$196.14	$196.15	$196.10
7 purchase totals =	$1,306.09		$1,422.7046	$1,422.70	$1,422.75	$1,422.60