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	$210.50	11.226%	$234.1307	$234.13	$234.15	$234.10
Purchase #2	$89.76	8.833%	$97.6885	$97.69	$97.70	$97.70
Purchase #3	$246.56	11.741%	$275.5086	$275.51	$275.50	$275.50
Purchase #4	$34.45	5.497%	$36.3437	$36.34	$36.35	$36.30
Purchase #5	$182.55	4.505%	$190.7739	$190.77	$190.75	$190.80
Purchase #6	$139.38	8.145%	$150.7325	$150.73	$150.75	$150.70
Purchase #7	$53.49	3.440%	$55.3301	$55.33	$55.35	$55.30
7 purchase totals =	$956.69		$1,040.5080	$1,040.50	$1,040.55	$1,040.40