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	$78.45	8.436%	$85.068	$85.07	$85.05	$85.10
Purchase #2	$218.68	12.279%	$245.5317	$245.53	$245.55	$245.50
Purchase #3	$232.99	4.427%	$243.3045	$243.30	$243.30	$243.30
Purchase #4	$12.73	6.117%	$13.5087	$13.51	$13.50	$13.50
Purchase #5	$82.49	11.385%	$91.8815	$91.88	$91.90	$91.90
Purchase #6	$99.64	5.328%	$104.9488	$104.95	$104.95	$104.90
Purchase #7	$81.75	11.379%	$91.0523	$91.05	$91.05	$91.10
7 purchase totals =	$806.73		$875.2955	$875.29	$875.30	$875.30