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	$45.32	13.448%	$51.4146	$51.41	$51.40	$51.40
Purchase #2	$7.38	13.215%	$8.3553	$8.36	$8.35	$8.40
Purchase #3	$134.49	10.444%	$148.5361	$148.54	$148.55	$148.50
Purchase #4	$147.44	11.397%	$164.2437	$164.24	$164.25	$164.20
Purchase #5	$239.57	12.402%	$269.2815	$269.28	$269.30	$269.30
Purchase #6	$195.66	7.222%	$209.7906	$209.79	$209.80	$209.80
Purchase #7	$81.70	9.596%	$89.5399	$89.54	$89.55	$89.50
7 purchase totals =	$851.56		$941.1617	$941.16	$941.20	$941.10