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	$247.54	9.428%	$270.8781	$270.88	$270.90	$270.90
Purchase #2	$223.47	6.506%	$238.009	$238.01	$238.00	$238.00
Purchase #3	$113.39	13.109%	$128.2543	$128.25	$128.25	$128.30
Purchase #4	$128.38	8.839%	$139.7275	$139.73	$139.75	$139.70
Purchase #5	$148.53	8.669%	$161.4061	$161.41	$161.40	$161.40
Purchase #6	$30.81	7.660%	$33.17	$33.17	$33.15	$33.20
Purchase #7	$82.94	10.755%	$91.8602	$91.86	$91.85	$91.90
7 purchase totals =	$975.06		$1,063.3052	$1,063.31	$1,063.30	$1,063.40