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	$28.31	12.315%	$31.7964	$31.80	$31.80	$31.80
Purchase #2	$245.69	11.431%	$273.7748	$273.77	$273.75	$273.80
Purchase #3	$130.77	8.119%	$141.3872	$141.39	$141.40	$141.40
Purchase #4	$36.92	11.258%	$41.0765	$41.08	$41.10	$41.10
Purchase #5	$192.45	8.154%	$208.1424	$208.14	$208.15	$208.10
Purchase #6	$35.90	4.866%	$37.6469	$37.65	$37.65	$37.60
Purchase #7	$83.31	7.276%	$89.3716	$89.37	$89.35	$89.40
7 purchase totals =	$753.35		$823.1958	$823.20	$823.20	$823.20