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	$129.69	6.340%	$137.9123	$137.91	$137.90	$137.90
Purchase #2	$250.86	6.614%	$267.4519	$267.45	$267.45	$267.50
Purchase #3	$162.93	3.565%	$168.7385	$168.74	$168.75	$168.70
Purchase #4	$185.54	9.826%	$203.7712	$203.77	$203.75	$203.80
Purchase #5	$168.33	8.631%	$182.8586	$182.86	$182.85	$182.90
Purchase #6	$100.76	8.247%	$109.0697	$109.07	$109.05	$109.10
Purchase #7	$10.90	11.115%	$12.1115	$12.11	$12.10	$12.10
7 purchase totals =	$1,009.01		$1,081.9137	$1,081.91	$1,081.85	$1,082.00