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	$169.85	9.616%	$186.1828	$186.18	$186.20	$186.20
Purchase #2	$88.39	12.872%	$99.7676	$99.77	$99.75	$99.80
Purchase #3	$34.27	9.410%	$37.4948	$37.49	$37.50	$37.50
Purchase #4	$212.37	12.315%	$238.5234	$238.52	$238.50	$238.50
Purchase #5	$66.39	4.160%	$69.1518	$69.15	$69.15	$69.20
Purchase #6	$245.46	9.414%	$268.5676	$268.57	$268.55	$268.60
Purchase #7	$91.82	6.779%	$98.0445	$98.04	$98.05	$98.00
7 purchase totals =	$908.55		$997.7325	$997.72	$997.70	$997.80