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	$128.25	12.378%	$144.1248	$144.12	$144.10	$144.10
Purchase #2	$180.72	13.625%	$205.3431	$205.34	$205.35	$205.30
Purchase #3	$45.49	12.440%	$51.149	$51.15	$51.15	$51.10
Purchase #4	$167.98	4.173%	$174.9898	$174.99	$175.00	$175.00
Purchase #5	$181.31	10.616%	$200.5579	$200.56	$200.55	$200.60
Purchase #6	$99.40	6.679%	$106.0389	$106.04	$106.05	$106.00
Purchase #7	$31.33	13.541%	$35.5724	$35.57	$35.55	$35.60
7 purchase totals =	$834.48		$917.7759	$917.77	$917.75	$917.70