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	$235.65	3.289%	$243.4005	$243.40	$243.40	$243.40
Purchase #2	$55.56	6.404%	$59.1181	$59.12	$59.10	$59.10
Purchase #3	$125.78	13.610%	$142.8987	$142.90	$142.90	$142.90
Purchase #4	$119.67	10.675%	$132.4448	$132.44	$132.45	$132.40
Purchase #5	$250.59	5.652%	$264.7533	$264.75	$264.75	$264.80
Purchase #6	$59.45	3.442%	$61.4963	$61.50	$61.50	$61.50
Purchase #7	$249.26	8.415%	$270.2352	$270.24	$270.25	$270.20
7 purchase totals =	$1,095.96		$1,174.3469	$1,174.35	$1,174.35	$1,174.30