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	$145.53	4.770%	$152.4718	$152.47	$152.45	$152.50
Purchase #2	$83.69	9.311%	$91.4824	$91.48	$91.50	$91.50
Purchase #3	$125.84	4.336%	$131.2964	$131.30	$131.30	$131.30
Purchase #4	$247.56	9.271%	$270.5113	$270.51	$270.50	$270.50
Purchase #5	$142.36	4.204%	$148.3448	$148.34	$148.35	$148.30
Purchase #6	$166.82	6.829%	$178.2121	$178.21	$178.20	$178.20
Purchase #7	$129.32	6.198%	$137.3353	$137.34	$137.35	$137.30
7 purchase totals =	$1,041.12		$1,109.6541	$1,109.65	$1,109.65	$1,109.60