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	$109.76	12.871%	$123.8872	$123.89	$123.90	$123.90
Purchase #2	$182.42	3.852%	$189.4468	$189.45	$189.45	$189.40
Purchase #3	$64.63	7.482%	$69.4656	$69.47	$69.45	$69.50
Purchase #4	$166.47	8.270%	$180.2371	$180.24	$180.25	$180.20
Purchase #5	$195.79	13.702%	$222.6171	$222.62	$222.60	$222.60
Purchase #6	$168.36	10.862%	$186.6473	$186.65	$186.65	$186.60
Purchase #7	$135.61	11.319%	$150.9597	$150.96	$150.95	$151.00
7 purchase totals =	$1,023.04		$1,123.2608	$1,123.28	$1,123.25	$1,123.20