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	$111.38	10.738%	$123.34	$123.34	$123.35	$123.30
Purchase #2	$77.64	9.550%	$85.0546	$85.05	$85.05	$85.10
Purchase #3	$175.36	7.839%	$189.1065	$189.11	$189.10	$189.10
Purchase #4	$63.98	13.776%	$72.7939	$72.79	$72.80	$72.80
Purchase #5	$162.36	5.665%	$171.5577	$171.56	$171.55	$171.60
Purchase #6	$192.70	6.750%	$205.7073	$205.71	$205.70	$205.70
Purchase #7	$99.26	3.777%	$103.0091	$103.01	$103.00	$103.00
7 purchase totals =	$882.68		$950.5691	$950.57	$950.55	$950.60