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	$119.90	3.331%	$123.8939	$123.89	$123.90	$123.90
Purchase #2	$19.61	8.271%	$21.2319	$21.23	$21.25	$21.20
Purchase #3	$81.79	8.698%	$88.9041	$88.90	$88.90	$88.90
Purchase #4	$37.67	6.647%	$40.1739	$40.17	$40.15	$40.20
Purchase #5	$196.94	12.208%	$220.9824	$220.98	$221.00	$221.00
Purchase #6	$184.61	6.625%	$196.8404	$196.84	$196.85	$196.80
Purchase #7	$83.81	7.238%	$89.8762	$89.88	$89.90	$89.90
7 purchase totals =	$724.33		$781.9028	$781.89	$781.95	$781.90