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	$133.51	3.615%	$138.3364	$138.34	$138.35	$138.30
Purchase #2	$223.33	4.402%	$233.161	$233.16	$233.15	$233.20
Purchase #3	$15.35	7.354%	$16.4788	$16.48	$16.50	$16.50
Purchase #4	$219.72	4.274%	$229.1108	$229.11	$229.10	$229.10
Purchase #5	$86.96	11.461%	$96.9265	$96.93	$96.95	$96.90
Purchase #6	$81.43	12.822%	$91.871	$91.87	$91.85	$91.90
Purchase #7	$85.43	4.554%	$89.3205	$89.32	$89.30	$89.30
7 purchase totals =	$845.73		$895.2050	$895.21	$895.20	$895.20