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	$79.98	3.741%	$82.9721	$82.97	$82.95	$83.00
Purchase #2	$121.49	9.279%	$132.7631	$132.76	$132.75	$132.80
Purchase #3	$31.37	9.698%	$34.4123	$34.41	$34.40	$34.40
Purchase #4	$130.77	3.148%	$134.8866	$134.89	$134.90	$134.90
Purchase #5	$88.59	11.743%	$98.9931	$98.99	$99.00	$99.00
Purchase #6	$56.64	4.225%	$59.033	$59.03	$59.05	$59.00
Purchase #7	$11.69	13.765%	$13.2991	$13.30	$13.30	$13.30
7 purchase totals =	$520.53		$556.3593	$556.35	$556.35	$556.40