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	$248.81	4.274%	$259.4441	$259.44	$259.45	$259.40
Purchase #2	$243.76	12.123%	$273.311	$273.31	$273.30	$273.30
Purchase #3	$26.96	8.116%	$29.1481	$29.15	$29.15	$29.10
Purchase #4	$79.47	7.562%	$85.4795	$85.48	$85.50	$85.50
Purchase #5	$199.93	11.699%	$223.3198	$223.32	$223.30	$223.30
Purchase #6	$71.48	8.233%	$77.3649	$77.36	$77.35	$77.40
Purchase #7	$96.83	12.852%	$109.2746	$109.27	$109.25	$109.30
7 purchase totals =	$967.24		$1,057.3420	$1,057.33	$1,057.30	$1,057.30