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	$140.60	4.657%	$147.1477	$147.15	$147.15	$147.10
Purchase #2	$189.46	12.115%	$212.4131	$212.41	$212.40	$212.40
Purchase #3	$179.59	9.473%	$196.6026	$196.60	$196.60	$196.60
Purchase #4	$244.82	12.112%	$274.4726	$274.47	$274.45	$274.50
Purchase #5	$159.41	3.239%	$164.5733	$164.57	$164.55	$164.60
Purchase #6	$60.97	7.333%	$65.4409	$65.44	$65.45	$65.40
Purchase #7	$28.81	6.249%	$30.6103	$30.61	$30.60	$30.60
7 purchase totals =	$1,003.66		$1,091.2605	$1,091.25	$1,091.20	$1,091.20