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	$86.96	13.350%	$98.5692	$98.57	$98.55	$98.60
Purchase #2	$89.48	8.294%	$96.9015	$96.90	$96.90	$96.90
Purchase #3	$180.54	10.323%	$199.1771	$199.18	$199.20	$199.20
Purchase #4	$75.85	12.804%	$85.5618	$85.56	$85.55	$85.60
Purchase #5	$49.49	6.794%	$52.8524	$52.85	$52.85	$52.90
Purchase #6	$96.65	13.850%	$110.036	$110.04	$110.05	$110.00
Purchase #7	$25.72	7.167%	$27.5634	$27.56	$27.55	$27.60
7 purchase totals =	$604.69		$670.6614	$670.66	$670.65	$670.80