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	$133.56	10.263%	$147.2673	$147.27	$147.25	$147.30
Purchase #2	$66.83	4.470%	$69.8173	$69.82	$69.80	$69.80
Purchase #3	$221.93	3.560%	$229.8307	$229.83	$229.85	$229.80
Purchase #4	$119.86	4.541%	$125.3028	$125.30	$125.30	$125.30
Purchase #5	$82.67	8.582%	$89.7647	$89.76	$89.75	$89.80
Purchase #6	$226.67	12.221%	$254.3713	$254.37	$254.35	$254.40
Purchase #7	$165.82	11.504%	$184.8959	$184.90	$184.90	$184.90
7 purchase totals =	$1,017.34		$1,101.2500	$1,101.25	$1,101.20	$1,101.30