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	$85.89	3.764%	$89.1229	$89.12	$89.10	$89.10
Purchase #2	$38.74	11.656%	$43.2555	$43.26	$43.25	$43.30
Purchase #3	$61.81	9.578%	$67.7302	$67.73	$67.75	$67.70
Purchase #4	$45.33	10.867%	$50.256	$50.26	$50.25	$50.30
Purchase #5	$103.83	5.820%	$109.8729	$109.87	$109.85	$109.90
Purchase #6	$200.86	10.624%	$222.1994	$222.20	$222.20	$222.20
Purchase #7	$228.58	9.497%	$250.2882	$250.29	$250.30	$250.30
7 purchase totals =	$765.04		$832.7251	$832.73	$832.70	$832.80