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	$232.78	5.468%	$245.5084	$245.51	$245.50	$245.50
Purchase #2	$136.76	8.480%	$148.3572	$148.36	$148.35	$148.40
Purchase #3	$164.33	11.360%	$182.9979	$183.00	$183.00	$183.00
Purchase #4	$99.45	12.511%	$111.8922	$111.89	$111.90	$111.90
Purchase #5	$29.27	8.477%	$31.7512	$31.75	$31.75	$31.80
Purchase #6	$92.70	5.488%	$97.7874	$97.79	$97.80	$97.80
Purchase #7	$92.71	7.753%	$99.8978	$99.90	$99.90	$99.90
7 purchase totals =	$848.00		$918.1921	$918.20	$918.20	$918.30