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	$240.39	4.226%	$250.5489	$250.55	$250.55	$250.50
Purchase #2	$197.56	10.588%	$218.4777	$218.48	$218.50	$218.50
Purchase #3	$100.83	12.487%	$113.4206	$113.42	$113.40	$113.40
Purchase #4	$58.30	9.874%	$64.0565	$64.06	$64.05	$64.10
Purchase #5	$77.70	3.356%	$80.3076	$80.31	$80.30	$80.30
Purchase #6	$190.89	11.814%	$213.4417	$213.44	$213.45	$213.40
Purchase #7	$97.56	11.797%	$109.0692	$109.07	$109.05	$109.10
7 purchase totals =	$963.23		$1,049.3222	$1,049.33	$1,049.30	$1,049.30