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	$240.91	9.697%	$264.271	$264.27	$264.25	$264.30
Purchase #2	$170.25	6.206%	$180.8157	$180.82	$180.80	$180.80
Purchase #3	$86.98	13.559%	$98.7736	$98.77	$98.75	$98.80
Purchase #4	$86.95	4.460%	$90.828	$90.83	$90.85	$90.80
Purchase #5	$104.74	6.671%	$111.7272	$111.73	$111.75	$111.70
Purchase #6	$19.57	8.274%	$21.1892	$21.19	$21.20	$21.20
Purchase #7	$40.46	5.648%	$42.7452	$42.75	$42.75	$42.70
7 purchase totals =	$749.86		$810.3499	$810.36	$810.35	$810.30