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	$8.73	7.223%	$9.3606	$9.36	$9.35	$9.40
Purchase #2	$94.45	9.600%	$103.5172	$103.52	$103.50	$103.50
Purchase #3	$165.69	3.425%	$171.3649	$171.36	$171.35	$171.40
Purchase #4	$72.37	10.715%	$80.1244	$80.12	$80.10	$80.10
Purchase #5	$244.89	10.111%	$269.6508	$269.65	$269.65	$269.70
Purchase #6	$161.48	13.499%	$183.2782	$183.28	$183.30	$183.30
Purchase #7	$206.42	7.805%	$222.5311	$222.53	$222.55	$222.50
7 purchase totals =	$954.03		$1,039.8272	$1,039.82	$1,039.80	$1,039.90