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	$78.65	8.585%	$85.4021	$85.40	$85.40	$85.40
Purchase #2	$94.84	4.774%	$99.3677	$99.37	$99.35	$99.40
Purchase #3	$64.96	9.818%	$71.3378	$71.34	$71.35	$71.30
Purchase #4	$8.39	8.157%	$9.0744	$9.07	$9.05	$9.10
Purchase #5	$31.97	11.336%	$35.5941	$35.59	$35.60	$35.60
Purchase #6	$28.96	8.315%	$31.368	$31.37	$31.35	$31.40
Purchase #7	$38.68	3.829%	$40.1611	$40.16	$40.15	$40.20
7 purchase totals =	$346.45		$372.3052	$372.30	$372.25	$372.40