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	$42.78	9.242%	$46.7337	$46.73	$46.75	$46.70
Purchase #2	$162.77	12.753%	$183.5281	$183.53	$183.55	$183.50
Purchase #3	$71.79	11.514%	$80.0559	$80.06	$80.05	$80.10
Purchase #4	$110.63	12.629%	$124.6015	$124.60	$124.60	$124.60
Purchase #5	$203.85	13.673%	$231.7224	$231.72	$231.70	$231.70
Purchase #6	$179.75	9.221%	$196.3247	$196.32	$196.30	$196.30
Purchase #7	$39.92	13.502%	$45.31	$45.31	$45.30	$45.30
7 purchase totals =	$811.49		$908.2763	$908.27	$908.25	$908.20