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	$234.64	3.222%	$242.2001	$242.20	$242.20	$242.20
Purchase #2	$84.70	9.501%	$92.7473	$92.75	$92.75	$92.70
Purchase #3	$190.36	9.796%	$209.0077	$209.01	$209.00	$209.00
Purchase #4	$78.28	6.515%	$83.3799	$83.38	$83.40	$83.40
Purchase #5	$104.50	5.107%	$109.8368	$109.84	$109.85	$109.80
Purchase #6	$79.72	12.216%	$89.4586	$89.46	$89.45	$89.50
Purchase #7	$109.29	12.752%	$123.2267	$123.23	$123.25	$123.20
7 purchase totals =	$881.49		$949.8571	$949.87	$949.90	$949.80