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	$32.86	12.714%	$37.0378	$37.04	$37.05	$37.00
Purchase #2	$186.87	10.543%	$206.5717	$206.57	$206.55	$206.60
Purchase #3	$55.66	9.659%	$61.0362	$61.04	$61.05	$61.00
Purchase #4	$209.56	13.800%	$238.4793	$238.48	$238.50	$238.50
Purchase #5	$166.41	3.344%	$171.9748	$171.97	$171.95	$172.00
Purchase #6	$63.49	12.827%	$71.6339	$71.63	$71.65	$71.60
Purchase #7	$18.76	11.221%	$20.8651	$20.87	$20.85	$20.90
7 purchase totals =	$733.61		$807.5988	$807.60	$807.60	$807.60