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	$51.29	7.462%	$55.1173	$55.12	$55.10	$55.10
Purchase #2	$161.64	4.175%	$168.3885	$168.39	$168.40	$168.40
Purchase #3	$229.49	6.228%	$243.7826	$243.78	$243.80	$243.80
Purchase #4	$88.78	8.707%	$96.5101	$96.51	$96.50	$96.50
Purchase #5	$80.86	10.430%	$89.2937	$89.29	$89.30	$89.30
Purchase #6	$11.58	8.448%	$12.5583	$12.56	$12.55	$12.60
Purchase #7	$156.93	5.433%	$165.456	$165.46	$165.45	$165.50
7 purchase totals =	$780.57		$831.1065	$831.11	$831.10	$831.20