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	$74.35	9.521%	$81.4289	$81.43	$81.45	$81.40
Purchase #2	$72.94	13.709%	$82.9393	$82.94	$82.95	$82.90
Purchase #3	$91.36	6.633%	$97.4199	$97.42	$97.40	$97.40
Purchase #4	$66.46	13.484%	$75.4215	$75.42	$75.40	$75.40
Purchase #5	$37.73	6.834%	$40.3085	$40.31	$40.30	$40.30
Purchase #6	$174.54	5.680%	$184.4539	$184.45	$184.45	$184.50
Purchase #7	$37.95	6.650%	$40.4737	$40.47	$40.45	$40.50
7 purchase totals =	$555.33		$602.4457	$602.44	$602.40	$602.40