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	$124.74	10.220%	$137.4884	$137.49	$137.50	$137.50
Purchase #2	$213.36	12.756%	$240.5762	$240.58	$240.60	$240.60
Purchase #3	$146.33	12.748%	$164.9841	$164.98	$165.00	$165.00
Purchase #4	$226.83	7.261%	$243.3001	$243.30	$243.30	$243.30
Purchase #5	$96.30	6.506%	$102.5653	$102.57	$102.55	$102.60
Purchase #6	$25.46	5.852%	$26.9499	$26.95	$26.95	$26.90
Purchase #7	$90.34	11.641%	$100.8565	$100.86	$100.85	$100.90
7 purchase totals =	$923.36		$1,016.7205	$1,016.73	$1,016.75	$1,016.80