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	$189.51	8.117%	$204.8925	$204.89	$204.90	$204.90
Purchase #2	$196.97	12.843%	$222.2669	$222.27	$222.25	$222.30
Purchase #3	$91.49	9.170%	$99.8796	$99.88	$99.90	$99.90
Purchase #4	$85.53	13.511%	$97.086	$97.09	$97.10	$97.10
Purchase #5	$26.67	9.234%	$29.1327	$29.13	$29.15	$29.10
Purchase #6	$39.88	6.664%	$42.5376	$42.54	$42.55	$42.50
Purchase #7	$237.83	4.765%	$249.1626	$249.16	$249.15	$249.20
7 purchase totals =	$867.88		$944.9579	$944.96	$945.00	$945.00