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	$179.69	6.458%	$191.2944	$191.29	$191.30	$191.30
Purchase #2	$125.76	13.441%	$142.6634	$142.66	$142.65	$142.70
Purchase #3	$162.61	10.672%	$179.9637	$179.96	$179.95	$180.00
Purchase #4	$250.57	4.579%	$262.0436	$262.04	$262.05	$262.00
Purchase #5	$89.88	5.227%	$94.578	$94.58	$94.60	$94.60
Purchase #6	$184.45	6.476%	$196.395	$196.40	$196.40	$196.40
Purchase #7	$159.91	9.704%	$175.4277	$175.43	$175.45	$175.40
7 purchase totals =	$1,152.87		$1,242.3658	$1,242.36	$1,242.40	$1,242.40