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	$7.43	12.371%	$8.3492	$8.35	$8.35	$8.30
Purchase #2	$33.52	11.150%	$37.2575	$37.26	$37.25	$37.30
Purchase #3	$136.63	7.511%	$146.8923	$146.89	$146.90	$146.90
Purchase #4	$82.52	10.179%	$90.9197	$90.92	$90.90	$90.90
Purchase #5	$237.33	10.113%	$261.3312	$261.33	$261.35	$261.30
Purchase #6	$59.52	10.408%	$65.7148	$65.71	$65.70	$65.70
Purchase #7	$42.25	3.770%	$43.8428	$43.84	$43.85	$43.80
7 purchase totals =	$599.20		$654.3075	$654.30	$654.30	$654.20