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	$108.52	8.718%	$117.9808	$117.98	$118.00	$118.00
Purchase #2	$64.33	4.654%	$67.3239	$67.32	$67.30	$67.30
Purchase #3	$92.71	13.306%	$105.046	$105.05	$105.05	$105.00
Purchase #4	$247.73	9.332%	$270.8482	$270.85	$270.85	$270.80
Purchase #5	$231.46	5.380%	$243.9125	$243.91	$243.90	$243.90
Purchase #6	$31.66	3.562%	$32.7877	$32.79	$32.80	$32.80
Purchase #7	$80.28	13.354%	$91.0006	$91.00	$91.00	$91.00
7 purchase totals =	$856.69		$928.8997	$928.90	$928.90	$928.80