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	$170.37	10.529%	$188.3083	$188.31	$188.30	$188.30
Purchase #2	$36.75	3.557%	$38.0572	$38.06	$38.05	$38.10
Purchase #3	$86.51	9.157%	$94.4317	$94.43	$94.45	$94.40
Purchase #4	$175.90	8.828%	$191.4285	$191.43	$191.45	$191.40
Purchase #5	$67.92	5.123%	$71.3995	$71.40	$71.40	$71.40
Purchase #6	$86.90	3.215%	$89.6938	$89.69	$89.70	$89.70
Purchase #7	$189.57	7.500%	$203.7878	$203.79	$203.80	$203.80
7 purchase totals =	$813.92		$877.1068	$877.11	$877.15	$877.10