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	$147.78	12.550%	$166.3264	$166.33	$166.35	$166.30
Purchase #2	$201.54	10.737%	$223.1793	$223.18	$223.20	$223.20
Purchase #3	$10.58	11.715%	$11.8194	$11.82	$11.80	$11.80
Purchase #4	$236.50	9.663%	$259.353	$259.35	$259.35	$259.40
Purchase #5	$158.53	10.424%	$175.0552	$175.06	$175.05	$175.10
Purchase #6	$148.47	10.827%	$164.5448	$164.54	$164.55	$164.50
Purchase #7	$177.73	7.162%	$190.459	$190.46	$190.45	$190.50
7 purchase totals =	$1,081.13		$1,190.7371	$1,190.74	$1,190.75	$1,190.80