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	$131.86	5.537%	$139.1611	$139.16	$139.15	$139.20
Purchase #2	$31.98	13.589%	$36.3258	$36.33	$36.35	$36.30
Purchase #3	$69.35	3.496%	$71.7745	$71.77	$71.75	$71.80
Purchase #4	$160.46	4.216%	$167.225	$167.23	$167.25	$167.20
Purchase #5	$249.54	10.350%	$275.3674	$275.37	$275.35	$275.40
Purchase #6	$90.47	3.132%	$93.3035	$93.30	$93.30	$93.30
Purchase #7	$81.42	5.143%	$85.6074	$85.61	$85.60	$85.60
7 purchase totals =	$815.08		$868.7647	$868.77	$868.75	$868.80