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	$91.40	8.112%	$98.8144	$98.81	$98.80	$98.80
Purchase #2	$169.45	4.266%	$176.6787	$176.68	$176.70	$176.70
Purchase #3	$147.41	3.340%	$152.3335	$152.33	$152.35	$152.30
Purchase #4	$75.53	12.714%	$85.1329	$85.13	$85.15	$85.10
Purchase #5	$86.68	3.259%	$89.5049	$89.50	$89.50	$89.50
Purchase #6	$41.56	9.854%	$45.6553	$45.66	$45.65	$45.70
Purchase #7	$249.27	11.385%	$277.6494	$277.65	$277.65	$277.60
7 purchase totals =	$861.30		$925.7691	$925.76	$925.80	$925.70