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	$101.53	7.548%	$109.1935	$109.19	$109.20	$109.20
Purchase #2	$182.63	7.804%	$196.8824	$196.88	$196.90	$196.90
Purchase #3	$210.51	8.864%	$229.1696	$229.17	$229.15	$229.20
Purchase #4	$204.74	8.360%	$221.8563	$221.86	$221.85	$221.90
Purchase #5	$151.71	11.115%	$168.5726	$168.57	$168.55	$168.60
Purchase #6	$212.58	3.200%	$219.3826	$219.38	$219.40	$219.40
Purchase #7	$229.56	10.848%	$254.4627	$254.46	$254.45	$254.50
7 purchase totals =	$1,293.26		$1,399.5197	$1,399.51	$1,399.50	$1,399.70