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	$28.55	12.457%	$32.1065	$32.11	$32.10	$32.10
Purchase #2	$42.33	6.841%	$45.2258	$45.23	$45.25	$45.20
Purchase #3	$189.44	6.572%	$201.89	$201.89	$201.90	$201.90
Purchase #4	$243.99	12.167%	$273.6763	$273.68	$273.70	$273.70
Purchase #5	$160.53	8.576%	$174.2971	$174.30	$174.30	$174.30
Purchase #6	$41.63	9.272%	$45.4899	$45.49	$45.50	$45.50
Purchase #7	$222.82	3.739%	$231.1512	$231.15	$231.15	$231.20
7 purchase totals =	$929.29		$1,003.8368	$1,003.85	$1,003.90	$1,003.90