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	$207.38	6.334%	$220.5154	$220.52	$220.50	$220.50
Purchase #2	$64.90	3.500%	$67.1715	$67.17	$67.15	$67.20
Purchase #3	$104.94	9.475%	$114.8831	$114.88	$114.90	$114.90
Purchase #4	$76.51	11.727%	$85.4823	$85.48	$85.50	$85.50
Purchase #5	$189.81	10.238%	$209.2427	$209.24	$209.25	$209.20
Purchase #6	$38.81	11.564%	$43.298	$43.30	$43.30	$43.30
Purchase #7	$242.38	13.502%	$275.1061	$275.11	$275.10	$275.10
7 purchase totals =	$924.73		$1,015.6991	$1,015.70	$1,015.70	$1,015.70