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	$55.59	9.814%	$61.0456	$61.05	$61.05	$61.00
Purchase #2	$43.98	6.780%	$46.9618	$46.96	$46.95	$47.00
Purchase #3	$107.91	8.758%	$117.3608	$117.36	$117.35	$117.40
Purchase #4	$180.75	8.466%	$196.0523	$196.05	$196.05	$196.10
Purchase #5	$230.55	6.377%	$245.2522	$245.25	$245.25	$245.30
Purchase #6	$63.49	13.467%	$72.0402	$72.04	$72.05	$72.00
Purchase #7	$104.58	13.838%	$119.0518	$119.05	$119.05	$119.10
7 purchase totals =	$786.85		$857.7647	$857.76	$857.75	$857.90