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	$243.44	4.432%	$254.2293	$254.23	$254.25	$254.20
Purchase #2	$175.78	7.780%	$189.4557	$189.46	$189.45	$189.50
Purchase #3	$148.77	4.736%	$155.8157	$155.82	$155.80	$155.80
Purchase #4	$91.31	9.531%	$100.0128	$100.01	$100.00	$100.00
Purchase #5	$152.26	9.237%	$166.3243	$166.32	$166.30	$166.30
Purchase #6	$170.42	5.140%	$179.1796	$179.18	$179.20	$179.20
Purchase #7	$39.34	5.535%	$41.5175	$41.52	$41.50	$41.50
7 purchase totals =	$1,021.32		$1,086.5349	$1,086.54	$1,086.50	$1,086.50