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	$7.61	3.483%	$7.8751	$7.88	$7.90	$7.90
Purchase #2	$17.42	4.861%	$18.2668	$18.27	$18.25	$18.30
Purchase #3	$84.39	12.462%	$94.9067	$94.91	$94.90	$94.90
Purchase #4	$186.44	13.365%	$211.3577	$211.36	$211.35	$211.40
Purchase #5	$110.42	11.442%	$123.0543	$123.05	$123.05	$123.10
Purchase #6	$50.36	10.309%	$55.5516	$55.55	$55.55	$55.60
Purchase #7	$55.34	3.544%	$57.3012	$57.30	$57.30	$57.30
7 purchase totals =	$511.98		$568.3134	$568.32	$568.30	$568.50