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	$129.44	3.776%	$134.3277	$134.33	$134.35	$134.30
Purchase #2	$101.85	6.860%	$108.8369	$108.84	$108.85	$108.80
Purchase #3	$234.65	6.571%	$250.0689	$250.07	$250.05	$250.10
Purchase #4	$188.41	10.864%	$208.8789	$208.88	$208.90	$208.90
Purchase #5	$82.93	3.516%	$85.8458	$85.85	$85.85	$85.80
Purchase #6	$215.92	6.333%	$229.5942	$229.59	$229.60	$229.60
Purchase #7	$96.90	9.756%	$106.3536	$106.35	$106.35	$106.40
7 purchase totals =	$1,050.10		$1,123.9060	$1,123.91	$1,123.95	$1,123.90