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	$240.97	12.489%	$271.0647	$271.06	$271.05	$271.10
Purchase #2	$46.33	9.134%	$50.5618	$50.56	$50.55	$50.60
Purchase #3	$85.33	13.500%	$96.8496	$96.85	$96.85	$96.80
Purchase #4	$135.52	7.442%	$145.6054	$145.61	$145.60	$145.60
Purchase #5	$38.73	12.478%	$43.5627	$43.56	$43.55	$43.60
Purchase #6	$35.59	7.695%	$38.3287	$38.33	$38.35	$38.30
Purchase #7	$83.96	6.103%	$89.0841	$89.08	$89.10	$89.10
7 purchase totals =	$666.43		$735.0570	$735.05	$735.05	$735.10