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	$121.76	8.309%	$131.877	$131.88	$131.90	$131.90
Purchase #2	$56.89	12.443%	$63.9688	$63.97	$63.95	$64.00
Purchase #3	$72.87	13.597%	$82.7781	$82.78	$82.80	$82.80
Purchase #4	$206.34	13.290%	$233.7626	$233.76	$233.75	$233.80
Purchase #5	$110.61	4.138%	$115.187	$115.19	$115.20	$115.20
Purchase #6	$167.33	9.349%	$182.9737	$182.97	$182.95	$183.00
Purchase #7	$113.90	12.257%	$127.8607	$127.86	$127.85	$127.90
7 purchase totals =	$849.70		$938.4079	$938.41	$938.40	$938.60