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	$73.73	9.165%	$80.4874	$80.49	$80.50	$80.50
Purchase #2	$133.81	5.843%	$141.6285	$141.63	$141.65	$141.60
Purchase #3	$103.77	6.401%	$110.4123	$110.41	$110.40	$110.40
Purchase #4	$96.45	11.424%	$107.4684	$107.47	$107.45	$107.50
Purchase #5	$33.71	11.702%	$37.6547	$37.65	$37.65	$37.70
Purchase #6	$156.89	6.148%	$166.5356	$166.54	$166.55	$166.50
Purchase #7	$120.75	5.225%	$127.0592	$127.06	$127.05	$127.10
7 purchase totals =	$719.11		$771.2461	$771.25	$771.25	$771.30