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	$147.89	5.179%	$155.5492	$155.55	$155.55	$155.50
Purchase #2	$120.99	12.417%	$136.0133	$136.01	$136.00	$136.00
Purchase #3	$231.74	10.370%	$255.7714	$255.77	$255.75	$255.80
Purchase #4	$41.47	13.825%	$47.2032	$47.20	$47.20	$47.20
Purchase #5	$85.78	12.688%	$96.6638	$96.66	$96.65	$96.70
Purchase #6	$175.25	13.167%	$198.3252	$198.33	$198.35	$198.30
Purchase #7	$109.84	3.627%	$113.8239	$113.82	$113.80	$113.80
7 purchase totals =	$912.96		$1,003.3500	$1,003.34	$1,003.30	$1,003.30