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	$249.77	10.587%	$276.2131	$276.21	$276.20	$276.20
Purchase #2	$105.70	3.812%	$109.7293	$109.73	$109.75	$109.70
Purchase #3	$70.34	11.811%	$78.6479	$78.65	$78.65	$78.60
Purchase #4	$81.78	8.391%	$88.6422	$88.64	$88.65	$88.60
Purchase #5	$150.89	3.648%	$156.3945	$156.39	$156.40	$156.40
Purchase #6	$246.50	7.711%	$265.5076	$265.51	$265.50	$265.50
Purchase #7	$104.57	4.330%	$109.0979	$109.10	$109.10	$109.10
7 purchase totals =	$1,009.55		$1,084.2325	$1,084.23	$1,084.25	$1,084.10