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	$243.75	13.755%	$277.2778	$277.28	$277.30	$277.30
Purchase #2	$144.28	5.727%	$152.5429	$152.54	$152.55	$152.50
Purchase #3	$36.36	7.672%	$39.1495	$39.15	$39.15	$39.10
Purchase #4	$131.57	6.228%	$139.7642	$139.76	$139.75	$139.80
Purchase #5	$167.55	7.626%	$180.3274	$180.33	$180.35	$180.30
Purchase #6	$37.77	6.846%	$40.3557	$40.36	$40.35	$40.40
Purchase #7	$90.79	6.255%	$96.4689	$96.47	$96.45	$96.50
7 purchase totals =	$852.07		$925.8864	$925.89	$925.90	$925.90