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	$104.31	7.510%	$112.1437	$112.14	$112.15	$112.10
Purchase #2	$97.88	5.112%	$102.8836	$102.88	$102.90	$102.90
Purchase #3	$106.33	5.732%	$112.4248	$112.42	$112.40	$112.40
Purchase #4	$100.34	9.855%	$110.2285	$110.23	$110.25	$110.20
Purchase #5	$183.73	6.613%	$195.8801	$195.88	$195.90	$195.90
Purchase #6	$84.33	7.472%	$90.6311	$90.63	$90.65	$90.60
Purchase #7	$66.28	5.384%	$69.8485	$69.85	$69.85	$69.80
7 purchase totals =	$743.20		$794.0403	$794.03	$794.10	$793.90