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	$128.69	5.759%	$136.1013	$136.10	$136.10	$136.10
Purchase #2	$53.99	4.173%	$56.243	$56.24	$56.25	$56.20
Purchase #3	$140.25	4.492%	$146.55	$146.55	$146.55	$146.60
Purchase #4	$219.78	4.112%	$228.8174	$228.82	$228.80	$228.80
Purchase #5	$57.73	13.183%	$65.3405	$65.34	$65.35	$65.30
Purchase #6	$130.59	12.441%	$146.8367	$146.84	$146.85	$146.80
Purchase #7	$200.50	11.466%	$223.4893	$223.49	$223.50	$223.50
7 purchase totals =	$931.53		$1,003.3782	$1,003.38	$1,003.40	$1,003.30