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	$112.73	7.442%	$121.1194	$121.12	$121.10	$121.10
Purchase #2	$104.54	4.476%	$109.2192	$109.22	$109.20	$109.20
Purchase #3	$55.38	7.410%	$59.4837	$59.48	$59.50	$59.50
Purchase #4	$176.52	10.506%	$195.0652	$195.07	$195.05	$195.10
Purchase #5	$168.96	9.660%	$185.2815	$185.28	$185.30	$185.30
Purchase #6	$79.43	9.179%	$86.7209	$86.72	$86.70	$86.70
Purchase #7	$15.37	5.740%	$16.2522	$16.25	$16.25	$16.30
7 purchase totals =	$712.93		$773.1421	$773.14	$773.10	$773.20