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	$205.72	8.351%	$222.8997	$222.90	$222.90	$222.90
Purchase #2	$55.34	7.645%	$59.5707	$59.57	$59.55	$59.60
Purchase #3	$91.92	13.489%	$104.3191	$104.32	$104.30	$104.30
Purchase #4	$215.78	8.854%	$234.8852	$234.89	$234.90	$234.90
Purchase #5	$36.44	13.256%	$41.2705	$41.27	$41.25	$41.30
Purchase #6	$7.44	11.650%	$8.3068	$8.31	$8.30	$8.30
Purchase #7	$110.75	9.393%	$121.1527	$121.15	$121.15	$121.20
7 purchase totals =	$723.39		$792.4047	$792.41	$792.35	$792.50