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	$38.56	11.224%	$42.888	$42.89	$42.90	$42.90
Purchase #2	$148.79	11.494%	$165.8919	$165.89	$165.90	$165.90
Purchase #3	$36.51	7.394%	$39.2095	$39.21	$39.20	$39.20
Purchase #4	$116.81	6.550%	$124.4611	$124.46	$124.45	$124.50
Purchase #5	$77.59	6.704%	$82.7916	$82.79	$82.80	$82.80
Purchase #6	$139.89	9.457%	$153.1194	$153.12	$153.10	$153.10
Purchase #7	$110.71	11.306%	$123.2269	$123.23	$123.25	$123.20
7 purchase totals =	$668.86		$731.5884	$731.59	$731.60	$731.60