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	$27.82	10.476%	$30.7344	$30.73	$30.75	$30.70
Purchase #2	$93.47	11.375%	$104.1022	$104.10	$104.10	$104.10
Purchase #3	$41.46	3.502%	$42.9119	$42.91	$42.90	$42.90
Purchase #4	$126.45	12.158%	$141.8238	$141.82	$141.80	$141.80
Purchase #5	$110.29	8.349%	$119.4981	$119.50	$119.50	$119.50
Purchase #6	$88.78	5.505%	$93.6673	$93.67	$93.65	$93.70
Purchase #7	$28.46	11.755%	$31.8055	$31.81	$31.80	$31.80
7 purchase totals =	$516.73		$564.5432	$564.54	$564.50	$564.50