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	$156.84	4.757%	$164.3009	$164.30	$164.30	$164.30
Purchase #2	$110.28	12.140%	$123.668	$123.67	$123.65	$123.70
Purchase #3	$25.32	13.651%	$28.7764	$28.78	$28.80	$28.80
Purchase #4	$59.63	3.257%	$61.5721	$61.57	$61.55	$61.60
Purchase #5	$41.69	5.154%	$43.8387	$43.84	$43.85	$43.80
Purchase #6	$71.39	12.110%	$80.0353	$80.04	$80.05	$80.00
Purchase #7	$219.65	10.759%	$243.2821	$243.28	$243.30	$243.30
7 purchase totals =	$684.80		$745.4735	$745.48	$745.50	$745.50