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	$30.62	8.234%	$33.1413	$33.14	$33.15	$33.10
Purchase #2	$98.56	10.651%	$109.0576	$109.06	$109.05	$109.10
Purchase #3	$86.60	3.747%	$89.8449	$89.84	$89.85	$89.80
Purchase #4	$32.48	11.222%	$36.1249	$36.12	$36.10	$36.10
Purchase #5	$229.59	3.681%	$238.0412	$238.04	$238.05	$238.00
Purchase #6	$79.58	11.580%	$88.7954	$88.80	$88.80	$88.80
Purchase #7	$196.68	6.518%	$209.4996	$209.50	$209.50	$209.50
7 purchase totals =	$754.11		$804.5049	$804.50	$804.50	$804.40