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	$115.52	13.516%	$131.1337	$131.13	$131.15	$131.10
Purchase #2	$26.35	9.504%	$28.8543	$28.85	$28.85	$28.90
Purchase #3	$92.50	7.350%	$99.2988	$99.30	$99.30	$99.30
Purchase #4	$38.95	4.470%	$40.6911	$40.69	$40.70	$40.70
Purchase #5	$179.92	3.290%	$185.8394	$185.84	$185.85	$185.80
Purchase #6	$186.86	9.115%	$203.8923	$203.89	$203.90	$203.90
Purchase #7	$194.59	3.350%	$201.1088	$201.11	$201.10	$201.10
7 purchase totals =	$834.69		$890.8184	$890.81	$890.85	$890.80