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	$74.69	7.783%	$80.5031	$80.50	$80.50	$80.50
Purchase #2	$87.37	6.824%	$93.3321	$93.33	$93.35	$93.30
Purchase #3	$176.75	6.496%	$188.2317	$188.23	$188.25	$188.20
Purchase #4	$204.50	9.150%	$223.2118	$223.21	$223.20	$223.20
Purchase #5	$82.31	11.221%	$91.546	$91.55	$91.55	$91.50
Purchase #6	$184.40	3.355%	$190.5866	$190.59	$190.60	$190.60
Purchase #7	$190.73	9.776%	$209.3758	$209.38	$209.40	$209.40
7 purchase totals =	$1,000.75		$1,076.7871	$1,076.79	$1,076.85	$1,076.70