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	$206.56	5.667%	$218.2658	$218.27	$218.25	$218.30
Purchase #2	$52.50	12.632%	$59.1318	$59.13	$59.15	$59.10
Purchase #3	$141.54	9.666%	$155.2213	$155.22	$155.20	$155.20
Purchase #4	$241.53	8.199%	$261.333	$261.33	$261.35	$261.30
Purchase #5	$171.30	10.757%	$189.7267	$189.73	$189.75	$189.70
Purchase #6	$28.78	4.287%	$30.0138	$30.01	$30.00	$30.00
Purchase #7	$92.90	4.191%	$96.7934	$96.79	$96.80	$96.80
7 purchase totals =	$935.11		$1,010.4858	$1,010.48	$1,010.50	$1,010.40