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	$35.43	3.320%	$36.6063	$36.61	$36.60	$36.60
Purchase #2	$99.54	5.616%	$105.1302	$105.13	$105.15	$105.10
Purchase #3	$237.49	11.365%	$264.4807	$264.48	$264.50	$264.50
Purchase #4	$147.90	11.841%	$165.4128	$165.41	$165.40	$165.40
Purchase #5	$170.57	3.193%	$176.0163	$176.02	$176.00	$176.00
Purchase #6	$234.74	10.173%	$258.6201	$258.62	$258.60	$258.60
Purchase #7	$81.29	5.319%	$85.6138	$85.61	$85.60	$85.60
7 purchase totals =	$1,006.96		$1,091.8802	$1,091.88	$1,091.85	$1,091.80