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	$164.90	3.301%	$170.3433	$170.34	$170.35	$170.30
Purchase #2	$62.86	11.528%	$70.1065	$70.11	$70.10	$70.10
Purchase #3	$29.52	13.134%	$33.3972	$33.40	$33.40	$33.40
Purchase #4	$137.89	13.253%	$156.1646	$156.16	$156.15	$156.20
Purchase #5	$196.55	11.624%	$219.397	$219.40	$219.40	$219.40
Purchase #6	$165.54	12.700%	$186.5636	$186.56	$186.55	$186.60
Purchase #7	$67.56	8.568%	$73.3485	$73.35	$73.35	$73.30
7 purchase totals =	$824.82		$909.3207	$909.32	$909.30	$909.30