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	$124.51	9.610%	$136.4754	$136.48	$136.50	$136.50
Purchase #2	$89.30	12.404%	$100.3768	$100.38	$100.40	$100.40
Purchase #3	$216.78	11.662%	$242.0609	$242.06	$242.05	$242.10
Purchase #4	$188.63	13.398%	$213.9026	$213.90	$213.90	$213.90
Purchase #5	$243.68	13.723%	$277.1202	$277.12	$277.10	$277.10
Purchase #6	$226.75	7.739%	$244.2982	$244.30	$244.30	$244.30
Purchase #7	$156.66	5.663%	$165.5317	$165.53	$165.55	$165.50
7 purchase totals =	$1,246.31		$1,379.7658	$1,379.77	$1,379.80	$1,379.80