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	$243.59	13.670%	$276.8888	$276.89	$276.90	$276.90
Purchase #2	$139.71	9.287%	$152.6849	$152.68	$152.70	$152.70
Purchase #3	$96.57	3.339%	$99.7945	$99.79	$99.80	$99.80
Purchase #4	$28.46	9.196%	$31.0772	$31.08	$31.10	$31.10
Purchase #5	$140.50	6.241%	$149.2686	$149.27	$149.25	$149.30
Purchase #6	$26.94	7.503%	$28.9613	$28.96	$28.95	$29.00
Purchase #7	$78.56	13.588%	$89.2347	$89.23	$89.25	$89.20
7 purchase totals =	$754.33		$827.9100	$827.90	$827.95	$828.00