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	$156.82	6.636%	$167.2266	$167.23	$167.25	$167.20
Purchase #2	$43.71	8.685%	$47.5062	$47.51	$47.50	$47.50
Purchase #3	$138.44	10.457%	$152.9167	$152.92	$152.90	$152.90
Purchase #4	$64.88	10.700%	$71.8222	$71.82	$71.80	$71.80
Purchase #5	$222.59	4.727%	$233.1118	$233.11	$233.10	$233.10
Purchase #6	$93.62	4.698%	$98.0183	$98.02	$98.00	$98.00
Purchase #7	$140.46	4.775%	$147.167	$147.17	$147.15	$147.20
7 purchase totals =	$860.52		$917.7688	$917.78	$917.70	$917.70