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	$150.34	12.277%	$168.7972	$168.80	$168.80	$168.80
Purchase #2	$39.94	6.584%	$42.5696	$42.57	$42.55	$42.60
Purchase #3	$165.37	8.687%	$179.7357	$179.74	$179.75	$179.70
Purchase #4	$41.44	3.695%	$42.9712	$42.97	$42.95	$43.00
Purchase #5	$38.29	11.589%	$42.7274	$42.73	$42.75	$42.70
Purchase #6	$63.72	11.478%	$71.0338	$71.03	$71.05	$71.00
Purchase #7	$232.66	11.351%	$259.0692	$259.07	$259.05	$259.10
7 purchase totals =	$731.76		$806.9041	$806.91	$806.90	$806.90