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	$174.97	6.264%	$185.9301	$185.93	$185.95	$185.90
Purchase #2	$37.59	13.260%	$42.5744	$42.57	$42.55	$42.60
Purchase #3	$182.64	11.399%	$203.4591	$203.46	$203.45	$203.50
Purchase #4	$48.59	11.616%	$54.2342	$54.23	$54.25	$54.20
Purchase #5	$74.91	6.740%	$79.9589	$79.96	$79.95	$80.00
Purchase #6	$151.57	8.453%	$164.3822	$164.38	$164.40	$164.40
Purchase #7	$57.80	6.639%	$61.6373	$61.64	$61.65	$61.60
7 purchase totals =	$728.07		$792.1762	$792.17	$792.20	$792.20