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	$152.67	12.220%	$171.3263	$171.33	$171.35	$171.30
Purchase #2	$140.77	12.347%	$158.1509	$158.15	$158.15	$158.20
Purchase #3	$221.86	11.276%	$246.8769	$246.88	$246.90	$246.90
Purchase #4	$53.70	11.251%	$59.7418	$59.74	$59.75	$59.70
Purchase #5	$96.74	13.454%	$109.7554	$109.76	$109.75	$109.80
Purchase #6	$154.55	12.746%	$174.2489	$174.25	$174.25	$174.20
Purchase #7	$110.38	9.439%	$120.7988	$120.80	$120.80	$120.80
7 purchase totals =	$930.67		$1,040.8990	$1,040.91	$1,040.95	$1,040.90