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	$72.54	10.173%	$79.9195	$79.92	$79.90	$79.90
Purchase #2	$37.41	10.102%	$41.1892	$41.19	$41.20	$41.20
Purchase #3	$156.88	7.463%	$168.588	$168.59	$168.60	$168.60
Purchase #4	$147.51	11.817%	$164.9413	$164.94	$164.95	$164.90
Purchase #5	$195.58	11.772%	$218.6037	$218.60	$218.60	$218.60
Purchase #6	$109.44	10.250%	$120.6576	$120.66	$120.65	$120.70
Purchase #7	$179.90	11.561%	$200.6982	$200.70	$200.70	$200.70
7 purchase totals =	$899.26		$994.5975	$994.60	$994.60	$994.60