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	$93.73	8.119%	$101.3399	$101.34	$101.35	$101.30
Purchase #2	$17.77	3.708%	$18.4289	$18.43	$18.45	$18.40
Purchase #3	$137.36	4.776%	$143.9203	$143.92	$143.90	$143.90
Purchase #4	$98.97	10.623%	$109.4836	$109.48	$109.50	$109.50
Purchase #5	$191.86	9.638%	$210.3515	$210.35	$210.35	$210.40
Purchase #6	$88.94	12.272%	$99.8547	$99.85	$99.85	$99.90
Purchase #7	$209.57	3.417%	$216.731	$216.73	$216.75	$216.70
7 purchase totals =	$838.20		$900.1099	$900.10	$900.15	$900.10