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	$145.51	13.338%	$164.9181	$164.92	$164.90	$164.90
Purchase #2	$181.42	6.352%	$192.9438	$192.94	$192.95	$192.90
Purchase #3	$246.98	7.236%	$264.8515	$264.85	$264.85	$264.90
Purchase #4	$134.82	11.167%	$149.8753	$149.88	$149.90	$149.90
Purchase #5	$145.73	11.221%	$162.0824	$162.08	$162.10	$162.10
Purchase #6	$240.76	13.442%	$273.123	$273.12	$273.10	$273.10
Purchase #7	$222.80	12.420%	$250.4718	$250.47	$250.45	$250.50
7 purchase totals =	$1,318.02		$1,458.2659	$1,458.26	$1,458.25	$1,458.30