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	$51.69	10.827%	$57.2865	$57.29	$57.30	$57.30
Purchase #2	$238.26	13.306%	$269.9629	$269.96	$269.95	$270.00
Purchase #3	$67.67	7.233%	$72.5646	$72.56	$72.55	$72.60
Purchase #4	$162.54	6.345%	$172.8532	$172.85	$172.85	$172.90
Purchase #5	$118.74	9.543%	$130.0714	$130.07	$130.05	$130.10
Purchase #6	$129.79	12.134%	$145.5387	$145.54	$145.55	$145.50
Purchase #7	$210.39	8.424%	$228.1133	$228.11	$228.10	$228.10
7 purchase totals =	$979.08		$1,076.3906	$1,076.38	$1,076.35	$1,076.50