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	$233.51	10.874%	$258.9019	$258.90	$258.90	$258.90
Purchase #2	$175.51	7.581%	$188.8154	$188.82	$188.80	$188.80
Purchase #3	$95.33	3.322%	$98.4969	$98.50	$98.50	$98.50
Purchase #4	$35.50	4.528%	$37.1074	$37.11	$37.10	$37.10
Purchase #5	$28.74	12.853%	$32.434	$32.43	$32.45	$32.40
Purchase #6	$104.56	10.668%	$115.7145	$115.71	$115.70	$115.70
Purchase #7	$23.90	13.438%	$27.1117	$27.11	$27.10	$27.10
7 purchase totals =	$697.05		$758.5818	$758.58	$758.55	$758.50