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	$186.38	7.762%	$200.8468	$200.85	$200.85	$200.80
Purchase #2	$248.81	8.658%	$270.352	$270.35	$270.35	$270.40
Purchase #3	$85.48	5.185%	$89.9121	$89.91	$89.90	$89.90
Purchase #4	$130.45	13.385%	$147.9107	$147.91	$147.90	$147.90
Purchase #5	$227.41	3.825%	$236.1084	$236.11	$236.10	$236.10
Purchase #6	$24.75	7.469%	$26.5986	$26.60	$26.60	$26.60
Purchase #7	$73.87	6.541%	$78.7018	$78.70	$78.70	$78.70
7 purchase totals =	$977.15		$1,050.4304	$1,050.43	$1,050.40	$1,050.40