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	$52.76	8.812%	$57.4092	$57.41	$57.40	$57.40
Purchase #2	$212.99	4.638%	$222.8685	$222.87	$222.85	$222.90
Purchase #3	$236.95	5.130%	$249.1055	$249.11	$249.10	$249.10
Purchase #4	$101.33	7.753%	$109.1861	$109.19	$109.20	$109.20
Purchase #5	$120.80	10.362%	$133.3173	$133.32	$133.30	$133.30
Purchase #6	$77.78	4.641%	$81.3898	$81.39	$81.40	$81.40
Purchase #7	$76.72	11.216%	$85.3249	$85.32	$85.30	$85.30
7 purchase totals =	$879.33		$938.6013	$938.61	$938.55	$938.60