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	$166.41	10.673%	$184.1709	$184.17	$184.15	$184.20
Purchase #2	$86.91	4.433%	$90.7627	$90.76	$90.75	$90.80
Purchase #3	$152.53	10.372%	$168.3504	$168.35	$168.35	$168.40
Purchase #4	$194.36	3.138%	$200.459	$200.46	$200.45	$200.50
Purchase #5	$186.33	9.776%	$204.5456	$204.55	$204.55	$204.50
Purchase #6	$112.41	13.766%	$127.8844	$127.88	$127.90	$127.90
Purchase #7	$24.64	5.270%	$25.9385	$25.94	$25.95	$25.90
7 purchase totals =	$923.59		$1,002.1115	$1,002.11	$1,002.10	$1,002.20