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	$46.31	12.872%	$52.271	$52.27	$52.25	$52.30
Purchase #2	$79.69	11.862%	$89.1428	$89.14	$89.15	$89.10
Purchase #3	$165.42	10.576%	$182.9148	$182.91	$182.90	$182.90
Purchase #4	$180.95	3.776%	$187.7827	$187.78	$187.80	$187.80
Purchase #5	$133.75	13.585%	$151.9199	$151.92	$151.90	$151.90
Purchase #6	$161.43	6.282%	$171.571	$171.57	$171.55	$171.60
Purchase #7	$59.73	13.488%	$67.7864	$67.79	$67.80	$67.80
7 purchase totals =	$827.28		$903.3886	$903.38	$903.35	$903.40