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	$146.44	12.732%	$165.0847	$165.08	$165.10	$165.10
Purchase #2	$159.33	10.704%	$176.3847	$176.38	$176.40	$176.40
Purchase #3	$30.39	8.293%	$32.9102	$32.91	$32.90	$32.90
Purchase #4	$151.31	13.270%	$171.3888	$171.39	$171.40	$171.40
Purchase #5	$78.73	8.656%	$85.5449	$85.54	$85.55	$85.50
Purchase #6	$136.82	7.682%	$147.3305	$147.33	$147.35	$147.30
Purchase #7	$129.70	7.345%	$139.2265	$139.23	$139.25	$139.20
7 purchase totals =	$832.72		$917.8703	$917.86	$917.95	$917.80