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	$28.74	13.287%	$32.5587	$32.56	$32.55	$32.60
Purchase #2	$86.86	12.275%	$97.5221	$97.52	$97.50	$97.50
Purchase #3	$125.54	3.517%	$129.9552	$129.96	$129.95	$130.00
Purchase #4	$171.76	6.439%	$182.8196	$182.82	$182.80	$182.80
Purchase #5	$238.31	7.349%	$255.8234	$255.82	$255.80	$255.80
Purchase #6	$51.79	13.121%	$58.5854	$58.59	$58.60	$58.60
Purchase #7	$96.39	3.485%	$99.7492	$99.75	$99.75	$99.70
7 purchase totals =	$799.39		$857.0136	$857.02	$856.95	$857.00