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	$25.80	7.330%	$27.6911	$27.69	$27.70	$27.70
Purchase #2	$112.45	11.471%	$125.3491	$125.35	$125.35	$125.30
Purchase #3	$68.54	6.327%	$72.8765	$72.88	$72.90	$72.90
Purchase #4	$41.77	10.866%	$46.3087	$46.31	$46.30	$46.30
Purchase #5	$85.25	5.165%	$89.6532	$89.65	$89.65	$89.70
Purchase #6	$168.70	8.381%	$182.8387	$182.84	$182.85	$182.80
Purchase #7	$225.53	9.706%	$247.4199	$247.42	$247.40	$247.40
7 purchase totals =	$728.04		$792.1372	$792.14	$792.15	$792.10