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	$121.84	4.546%	$127.3788	$127.38	$127.40	$127.40
Purchase #2	$118.67	7.121%	$127.1205	$127.12	$127.10	$127.10
Purchase #3	$182.89	10.127%	$201.4113	$201.41	$201.40	$201.40
Purchase #4	$82.30	8.444%	$89.2494	$89.25	$89.25	$89.20
Purchase #5	$84.71	9.797%	$93.009	$93.01	$93.00	$93.00
Purchase #6	$135.51	4.841%	$142.07	$142.07	$142.05	$142.10
Purchase #7	$170.38	11.124%	$189.3331	$189.33	$189.35	$189.30
7 purchase totals =	$896.30		$969.5721	$969.57	$969.55	$969.50