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	$19.39	10.498%	$21.4256	$21.43	$21.45	$21.40
Purchase #2	$161.36	7.871%	$174.0606	$174.06	$174.05	$174.10
Purchase #3	$147.38	12.700%	$166.0973	$166.10	$166.10	$166.10
Purchase #4	$191.56	3.642%	$198.5366	$198.54	$198.55	$198.50
Purchase #5	$129.44	8.743%	$140.7569	$140.76	$140.75	$140.80
Purchase #6	$228.90	10.836%	$253.7036	$253.70	$253.70	$253.70
Purchase #7	$57.56	11.648%	$64.2646	$64.26	$64.25	$64.30
7 purchase totals =	$935.59		$1,018.8452	$1,018.85	$1,018.85	$1,018.90