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	$79.31	7.854%	$85.539	$85.54	$85.55	$85.50
Purchase #2	$77.91	9.817%	$85.5584	$85.56	$85.55	$85.60
Purchase #3	$28.88	10.505%	$31.9138	$31.91	$31.90	$31.90
Purchase #4	$73.83	6.301%	$78.482	$78.48	$78.50	$78.50
Purchase #5	$191.56	8.816%	$208.4479	$208.45	$208.45	$208.40
Purchase #6	$228.39	4.327%	$238.2724	$238.27	$238.25	$238.30
Purchase #7	$140.43	10.451%	$155.1063	$155.11	$155.10	$155.10
7 purchase totals =	$820.31		$883.3198	$883.32	$883.30	$883.30