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	$223.90	11.797%	$250.3135	$250.31	$250.30	$250.30
Purchase #2	$63.54	11.807%	$71.0422	$71.04	$71.05	$71.00
Purchase #3	$38.74	7.150%	$41.5099	$41.51	$41.50	$41.50
Purchase #4	$88.55	13.788%	$100.7593	$100.76	$100.75	$100.80
Purchase #5	$8.65	3.593%	$8.9608	$8.96	$8.95	$9.00
Purchase #6	$231.84	7.463%	$249.1422	$249.14	$249.15	$249.10
Purchase #7	$115.92	13.108%	$131.1148	$131.11	$131.10	$131.10
7 purchase totals =	$771.14		$852.8427	$852.83	$852.80	$852.80