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	$37.70	10.145%	$41.5247	$41.52	$41.50	$41.50
Purchase #2	$119.84	9.578%	$131.3183	$131.32	$131.30	$131.30
Purchase #3	$229.91	6.260%	$244.3024	$244.30	$244.30	$244.30
Purchase #4	$16.56	13.320%	$18.7658	$18.77	$18.75	$18.80
Purchase #5	$238.57	13.207%	$270.0779	$270.08	$270.10	$270.10
Purchase #6	$152.92	12.109%	$171.4371	$171.44	$171.45	$171.40
Purchase #7	$98.81	4.410%	$103.1675	$103.17	$103.15	$103.20
7 purchase totals =	$894.31		$980.5937	$980.60	$980.55	$980.60