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	$152.88	11.281%	$170.1264	$170.13	$170.15	$170.10
Purchase #2	$203.51	10.755%	$225.3975	$225.40	$225.40	$225.40
Purchase #3	$37.27	11.585%	$41.5877	$41.59	$41.60	$41.60
Purchase #4	$101.96	7.320%	$109.4235	$109.42	$109.40	$109.40
Purchase #5	$238.98	13.765%	$271.8756	$271.88	$271.90	$271.90
Purchase #6	$196.92	12.378%	$221.2948	$221.29	$221.30	$221.30
Purchase #7	$200.53	4.448%	$209.4496	$209.45	$209.45	$209.40
7 purchase totals =	$1,132.05		$1,249.1551	$1,249.16	$1,249.20	$1,249.10