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	$92.45	12.404%	$103.9175	$103.92	$103.90	$103.90
Purchase #2	$53.79	3.721%	$55.7915	$55.79	$55.80	$55.80
Purchase #3	$74.53	11.191%	$82.8707	$82.87	$82.85	$82.90
Purchase #4	$149.59	6.813%	$159.7816	$159.78	$159.80	$159.80
Purchase #5	$118.41	10.740%	$131.1272	$131.13	$131.15	$131.10
Purchase #6	$98.53	12.215%	$110.5654	$110.57	$110.55	$110.60
Purchase #7	$194.73	8.306%	$210.9043	$210.90	$210.90	$210.90
7 purchase totals =	$782.03		$854.9582	$854.96	$854.95	$855.00