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	$182.43	11.562%	$203.5226	$203.52	$203.50	$203.50
Purchase #2	$23.33	8.122%	$25.2249	$25.22	$25.20	$25.20
Purchase #3	$176.34	8.515%	$191.3554	$191.36	$191.35	$191.40
Purchase #4	$14.76	13.714%	$16.7842	$16.78	$16.80	$16.80
Purchase #5	$85.46	4.760%	$89.5279	$89.53	$89.55	$89.50
Purchase #6	$65.88	10.655%	$72.8995	$72.90	$72.90	$72.90
Purchase #7	$55.32	7.844%	$59.6593	$59.66	$59.65	$59.70
7 purchase totals =	$603.52		$658.9738	$658.97	$658.95	$659.00