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	$112.57	10.410%	$124.2885	$124.29	$124.30	$124.30
Purchase #2	$57.63	13.566%	$65.4481	$65.45	$65.45	$65.40
Purchase #3	$159.79	7.144%	$171.2054	$171.21	$171.20	$171.20
Purchase #4	$66.51	7.376%	$71.4158	$71.42	$71.40	$71.40
Purchase #5	$233.73	10.709%	$258.7601	$258.76	$258.75	$258.80
Purchase #6	$50.91	10.427%	$56.2184	$56.22	$56.20	$56.20
Purchase #7	$35.82	5.489%	$37.7862	$37.79	$37.80	$37.80
7 purchase totals =	$716.96		$785.1225	$785.14	$785.10	$785.10