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	$205.53	7.485%	$220.9139	$220.91	$220.90	$220.90
Purchase #2	$30.45	11.226%	$33.8683	$33.87	$33.85	$33.90
Purchase #3	$209.71	6.686%	$223.7312	$223.73	$223.75	$223.70
Purchase #4	$98.46	12.839%	$111.1013	$111.10	$111.10	$111.10
Purchase #5	$72.96	13.512%	$82.8184	$82.82	$82.80	$82.80
Purchase #6	$141.63	10.108%	$155.946	$155.95	$155.95	$155.90
Purchase #7	$145.54	13.604%	$165.3393	$165.34	$165.35	$165.30
7 purchase totals =	$904.28		$993.7184	$993.72	$993.70	$993.60