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	$19.80	6.697%	$21.126	$21.13	$21.15	$21.10
Purchase #2	$86.41	6.305%	$91.8582	$91.86	$91.85	$91.90
Purchase #3	$169.88	5.740%	$179.6311	$179.63	$179.65	$179.60
Purchase #4	$27.34	13.250%	$30.9626	$30.96	$30.95	$31.00
Purchase #5	$30.33	11.533%	$33.828	$33.83	$33.85	$33.80
Purchase #6	$36.73	7.340%	$39.426	$39.43	$39.45	$39.40
Purchase #7	$54.48	8.339%	$59.0231	$59.02	$59.00	$59.00
7 purchase totals =	$424.97		$455.8550	$455.86	$455.90	$455.80